lld template 7april05 (1)

Cisco Systems Advanced Services

Low Level Design Template

Version 0.1

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2

THE SPECIFICATIONS AND INFORMATION REGARDING THE PRODUCTS IN THIS MANUAL ARE SUBJECT TO CHANGE WITHOUT NOTICE. ALL STATEMENTS, INFORMATION, AND RECOMMENDATIONS IN THIS MANUAL ARE BELIEVED TO BE ACCURATE BUT ARE PRESENTED WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED. USERS MUST TAKE FULL RESPONSIBILITY FOR THEIR APPLICATION OF ANY PRODUCTS.

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The following information is for FCC compliance of Class A devices: This equipment has been tested and found to comply with the limits for a Class A digital device, pursuant to part 15 of the FCC rules. These limits are designed to provide reasonable protection against harmful interference when the equipment is operated in a commercial environment. This equipment generates, uses, and can radiate radio-frequency energy and, if not installed and used in accordance with the instruction manual, may cause harmful interference to radio communications. Operation of this equipment in a residential area is likely to cause harmful interference, in which case users will be required to correct the interference at their own expense.

The following information is for FCC compliance of Class B devices: The equipment described in this manual generates and may radiate radio-frequency energy. If it is not installed in accordance with Cisco’s installation instructions, it may cause interference with radio and television reception. This equipment has been tested and found to comply with the limits for a Class B digital device in accordance with the specifications in part 15 of the FCC rules. These specifications are designed to provide reasonable protection against such interference in a residential installation. However, there is no guarantee that interference will not occur in a particular installation.

You can determine whether your equipment is causing interference by turning it off. If the interference stops, it was probably caused by the Cisco equipment or one of its peripheral devices. If the equipment causes interference to radio or television reception, try to correct the interference by using one or more of the following measures:

Turn the television or radio antenna until the interference stops.

Move the equipment to one side or the other of the television or radio.

Move the equipment farther away from the television or radio.

Plug the equipment into an outlet that is on a different circuit from the television or radio. (That is, make certain the equipment and the television or radio are on circuits controlled by different circuit breakers or fuses.)

Modifications to this product not authorized by Cisco Systems, Inc. could void the FCC approval and negate your authority to operate the product.

The following third-party software may be included with your product and will be subject to the software license agreement:

CiscoWorks software and documentation are based in part on HP OpenView under license from the Hewlett-Packard Company. HP OpenView is a trademark of the Hewlett-Packard Company. Copyright 1992, 1993 Hewlett-Packard Company.

The Cisco implementation of TCP header compression is an adaptation of a program developed by the University of California, Berkeley (UCB) as part of UCB’s public domain version of the UNIX operating system. All rights reserved. Copyright 1981, Regents of the University of California.

Network Time Protocol (NTP). Copyright 1992, David L. Mills. The University of Delaware makes no representations about the suitability of this software for any purpose.

Point-to-Point Protocol. Copyright 1989, Carnegie-Mellon University. All rights reserved. The name of the University may not be used to endorse or promote products derived from this software without specific prior written permission.

The Cisco implementation of TN3270 is an adaptation of the TN3270, curses, and termcap programs developed by the University of California, Berkeley (UCB) as part of the UCB’s public domain version of the UNIX operating system. All rights reserved. Copyright 1981-1988, Regents of the University of California.

Cisco incorporates Fastmac and TrueView software and the RingRunner chip in some Token Ring products. Fastmac software is licensed to Cisco by Madge Networks Limited, and the RingRunner chip is licensed to Cisco by Madge NV. Fastmac, RingRunner, and TrueView are trademarks and in some jurisdictions registered trademarks of Madge Networks Limited. Copyright 1995, Madge Networks Limited. All rights reserved.

Xremote is a trademark of Network Computing Devices, Inc. Copyright 1989, Network Computing Devices, Inc., Mountain View, California. NCD makes no representations about the suitability of this software for any purpose.

The X Window System is a trademark of the X Consortium, Cambridge, Massachusetts. All rights reserved.

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INTELLECTUAL PROPERTY RIGHTS:THIS DOCUMENT CONTAINS VALUABLE TRADE SECRETS AND CONFIDENTIAL INFORMATION OF CISCO SYSTEMS, INC. AND IT’S SUPPLIERS, AND SHALL NOT BE DISCLOSED TO ANY PERSON, ORGANIZATION, OR ENTITY UNLESS SUCH DISCLOSURE IS SUBJECT TO THE PROVISIONS OF A WRITTEN NON-DISCLOSURE AND PROPRIETARY RIGHTS AGREEMENT OR INTELLECTUAL PROPERTY LICENSE AGREEMENT APPROVED BY CISCO SYSTEMS, INC. THE DISTRIBUTION OF THIS DOCUMENT DOES NOT GRANT ANY LICENSE IN OR RIGHTS, IN WHOLE OR IN PART, TO THE CONTENT, THE PRODUCT(S), TECHNOLOGY OF INTELLECTUAL PROPERTY DESCRIBED HEREIN.

Low Level Design TemplateCopyright 2001-2, Cisco Systems, Inc.All rights reserved.COMMERCIAL IN CONFIDENCE.

Contents

Contents........................................................................................................................................ 3

Tables.......................................................................................................................................... 11

Figures........................................................................................................................................ 12

Document Control...................................................................................................................... 14

History.................................................................................................................................... 14

Review.................................................................................................................................... 15

Design Acceptance...............................................................................................................16

About This Design Document...................................................................................................17

Document Purpose...............................................................................................................17

Scope..................................................................................................................................... 17

Document Usage Guidelines................................................................................................17

Assumptions and Caveats....................................................................................................18

Related Documents...............................................................................................................18

Network Overview...................................................................................................................... 19

Network Topology................................................................................................................. 19

WAN Overview..................................................................................................................................19

Network Infrastructure..........................................................................................................19

Core.....................................................................................................................................................19

Edge....................................................................................................................................................19

Access.................................................................................................................................................19

Traffic Flow and Characteristic............................................................................................20

Existing Services and SLAs.................................................................................................20

Proposed Network Architecture................................................................................................21

Design Considerations.........................................................................................................21

MPLS Network Architecture..............................................................................................................21

Quality-of-Service..............................................................................................................................22

MPLS/VPN Services..........................................................................................................................22

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Contents

Detailed Naming and Addressing Specifications...............................................................23

BGP AS Number................................................................................................................................23

<Customer Name> Routers.....................................................................................................23

Customer Edge (CE) Routers..................................................................................................23

DNS domain name..................................................................................................................23

IP Addressing......................................................................................................................................23

Loopbacks...............................................................................................................................23

Backbone Links.......................................................................................................................24

Existing Routers......................................................................................................................24

MPLS/VPN Access Connections............................................................................................24

Internet Access Connections...................................................................................................24

IP-SLA.....................................................................................................................................24

MPLS/VPN Attributes........................................................................................................................24

VRF Name...............................................................................................................................24

RD...........................................................................................................................................25

RT............................................................................................................................................25

SOO.........................................................................................................................................25

BGP AS Numbers...................................................................................................................25

Deployment Guidelines..............................................................................................................26

Physical Network Design......................................................................................................26

Layer-2 Transport Media....................................................................................................................26

Central Office Bratislava [BA]...........................................................................................................27

Peering Layer..........................................................................................................................28

Core Layer...............................................................................................................................31

Aggregation Layer...................................................................................................................33

Access Layer...........................................................................................................................37

Central Office Banska Bystrica [BB].................................................................................................39

Central Office Kosice [KE]................................................................................................................43

Regional PoPs.....................................................................................................................................47

Hardware/Software Release Table.....................................................................................................51

Logical Network Design.............................................................................................................53

IGP Routing – (OSPF or ISIS)...............................................................................................53

The Role of OSPF in <Customer name> MPLS network..................................................................53

OSPF Areas........................................................................................................................................54

OSPF Authentication..........................................................................................................................55

Loopback Addresses...........................................................................................................................55

OSPF Area Summarization.................................................................................................................55

OSPF Costs.........................................................................................................................................55

Designated and Backup Designated Routers......................................................................................56

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Contents

Default Routes....................................................................................................................................56

OSPF Convergence.............................................................................................................................56

OSPF DNS Lookup............................................................................................................................57

OSPF Configuration Template...........................................................................................................58

OSPF Deployment Recommendations Summary for the <CUSTOMER NAME> network.............58

Backbone Routing and Label Distribution Protocols.........................................58

Cisco Express Forwarding (CEF) Switching......................................................................................59

Label Distribution Protocol (LDP).....................................................................................................59

Interface MTU size............................................................................................................59

LDP Configuration and Design Recommendations..............................................60

Network Services....................................................................................................................... 62

MPLS/VPN Services..............................................................................................................62

MPLS-VPN.........................................................................................................................................62

MP-iBGP4 (Multi-protocol iBGP) Implementation...........................................................................63

Distribution of VPN Routing Information..............................................................................63

Use of VPNv4 Route Reflectors.............................................................................................64

Autonomous System Number......................................................................................67

MP-iBGP Authentication..................................................................................................67

Use of BGP Peer-groups.........................................................................................................68

Use of Path MTU discovery....................................................................................................68

Increasing Interface Input queue and SPD thresholds.............................................................68

MP-BGP Configuration.....................................................................................................69

Creating VRF Definitions...............................................................................................70

VRF Name..........................................................................................................................................70

Route-Distinguisher............................................................................................................................70

Route-distinguisher Allocation schemes and Recommendations...........................................70

VPN Route Target Communities........................................................................................................73

VPN Topologies.................................................................................................................74

Full Mesh............................................................................................................................................74

Hub and Spoke....................................................................................................................................74

Exranets..............................................................................................................................................74

Customers with Unique Addresses...............................................................................................74

Customers with Overlapping Addresses.......................................................................................75

Extranet NAT at a Common Service Point...................................................................................75

Extranet NAT at Customer Edge..................................................................................................75

Controlling route exports in extranets...........................................................................................75

PE-CE Routing Implementation................................................................................................76

Connectivity via Static Routing............................................................................................76

Routing Stability......................................................................................................................77

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Contents

RIPv2 configuration (PE to CE)............................................................................................77

PE Configuration................................................................................................................................77

CE Configuration................................................................................................................................78

eBGP configuration (PE to CE)............................................................................................78

Configuration at the PE......................................................................................................................78

Unique AS per customer site...................................................................................................78

Single AS for all customer sites..............................................................................................79

AS-Override............................................................................................................................80

Site-of-Origin..........................................................................................................................81

Routing Stability......................................................................................................................81

Controlling number of VRF routes.....................................................................................................82

Additional MPLS VPN Services.................................................................................................84

Internet Access for MPLS/VPN customers..............................................................84

Separate CEs for Internet Access and VPN Access...........................................................................84

Low-cost Internet Access (1CE + one/two access links)....................................................................85

Shared vrf-aware services...........................................................................................87

Network Address Translation for MPLS/VPN customers..................................................................87

Connecting Downstream ISPs to PE routers......................................................................................88

Remote Access (ASWAN/Security, Dial, DSL, Cable)..........................................89

Wireless............................................................................................................................... 89

VOIP...................................................................................................................................... 89

Inter-AS/CsC....................................................................................................................... 89

Traffic Engineering and Fast Reroute Technology Overview.................................................90

Traffic Engineering Basics...................................................................................................90

Traffic Trunk Attributes.........................................................................................................92

Bandwidth...........................................................................................................................................92

Path Selection Policy..........................................................................................................................92

Resource Class Affinity......................................................................................................................92

Adaptability........................................................................................................................................92

Resilience............................................................................................................................................92

Priority................................................................................................................................................93

Resource Attributes..............................................................................................................93

Available Bandwidth..........................................................................................................................93

Resource Class....................................................................................................................................93

Path Selection........................................................................................................................ 93

Path Setup.............................................................................................................................. 94

Link Protection (FRR) Basics...............................................................................................95

Increased Reliability for IP Services..................................................................................................97

High Scalability Solution....................................................................................................................97

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Contents

TE/TE-FRR Design...................................................................................................................... 98

Deciding on the tunnel topology and tunnel types............................................................98

How to Route Traffic Into TE Tunnels..................................................................................98

Policy Based Routing.........................................................................................................................98

Static Routing Into Tunnels................................................................................................................98

Auto-Route.........................................................................................................................................99

Forwarding Adjacency......................................................................................................................101

Using Directed LDP Sessions............................................................................................102

Number of Protected Prefixes............................................................................................102

“3” Implementation Of TE-FRR...............................................................................................105

“3” Network Architecture....................................................................................................105

Introduction.......................................................................................................................................105

TE-FRR Design................................................................................................................................106

Primary Tunnels..........................................................................................................................107

Backup Tunnels...........................................................................................................................107

Sample configurations......................................................................................................................109

Generic Global Commands.........................................................................................................109

Birmingham P Router.................................................................................................................109

Quality of Service................................................................................................................112

Introduction.......................................................................................................................................112

Differentiated Services Model – Introduction..................................................................................113

Default PHB..........................................................................................................................115

Class-Selector PHB:..............................................................................................................115

Assured Forwarding PHB.....................................................................................................116

Expedited Forwarding PHB..................................................................................................117

QoS and VoIP........................................................................................................................118

Interleaving mechanisms: FRF.12 or MLPPP / LFI..............................................................120

Delay Model..........................................................................................................................122

QoS in an MPLS network.....................................................................................................123

DiffServ Aware TE...........................................................................................................................124

ST QoS design – An Overview........................................................................................................124

CE-to-PE QoS mechanisms (applied on the CE) – PPP or HDLC...................................................126

Classification.........................................................................................................................126

Marking.................................................................................................................................128

Policing..................................................................................................................................131

Class Queuing........................................................................................................................133

Congestion avoidance............................................................................................................134

SAA-to-PE QoS mechanisms (applied on the SAA)............................................................143

CE-to-PE QoS mechanisms (applied on the PE) – PPP or HDLC...................................................144

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Contents

Classification.........................................................................................................................144

Marking.................................................................................................................................144

Policing..................................................................................................................................145

Unmanaged CEs and Unmanaged Internet CPEs..................................................................145

SAA Routers..........................................................................................................................146

PE-to-P QoS mechanisms (applied on the PE).................................................................................147

Classification.........................................................................................................................147

Marking.................................................................................................................................147

Class queuing........................................................................................................................147


PE-P, P-P and P-PE QoS mechanisms (applied on the P)................................................................149

Class Queuing (MDRR)........................................................................................................149

Congestion management.......................................................................................................152

PE to CE QoS mechanisms (applied on the PE)...............................................................................154

Classification.........................................................................................................................154

Class queuing........................................................................................................................154


QoS mechanisms on ATM PVCs (applied on the CE and PE)........................................................155

High Availability....................................................................................................................... 158

Security..................................................................................................................................... 159

Password Management.....................................................................................................................159

Console Ports....................................................................................................................................160

Controlling TTY’s............................................................................................................................160

Controlling VTYs and Ensuring VTY Availability..........................................................................160

Logging.............................................................................................................................................161

Saving logging information...................................................................................................162

Recording Access List Violations.........................................................................................162

Anti-spoofing....................................................................................................................................162

Anti-spoofing with packet filters...........................................................................................163

Controlling Directed Broadcasts.......................................................................................................164

IP Source Routing.............................................................................................................................164

ICMP Redirects................................................................................................................................165

CDP...................................................................................................................................................165

NTP...................................................................................................................................................165

Network Management..............................................................................................................167

Appendix I................................................................................................................................. 168

Appendix II................................................................................................................................. 169

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Contents

Tables

Table 1 Revision History 13

Table 2 Revision Review 14

Table 6 PE-P Connectivity in CO BA 32

Table 7 Software Release Table 50

Table 8 Proposed OSPF Metrics 54

Table 9 OSPF Timer Default Values 56

Table 5 RT/RD Allocation 73

Table 6 BGP Timer Definitions 81

Table 3 Tunnel Provisioning 107

Table 14 Class-Selector PHBs 115

Table 15 Serialisation delay [ms] as function of link speed and packet size 118

Table 16 Recommended fragment size 120

Table 17 The components of the end-to-end delay model 121

Table 18 CoS Mechanisms Overview 124

Table 19 NB and EB settings 131

Table 20 WRED Settings for Business Class. 138

Table 21 WRED Settings for Streaming Class. 138

Table 22 WRED Settings for Standard Class. 139

Table 23 WRED - exponential weighting constant 141

Table 24 MDRR weights 149

Table 25 WRED Setings for Business Class (ENG-2 GSR) 152

Table 26 WRED Setings for Streaming Class (ENG-2 GSR) 152

Table 27 WRED Setings for Standard Class (ENG-2 GSR) 152

Table 28 ATM Overhead 155

Table 29 LLQ bandwidths and ATM 155

Figures

Figure 1 <Company’s name> network – WAN topology 19

Figure 2 Architecture of CO BA 28

Figure 3 HW configuration of ba2-igw-2 29

Figure 4 HW configuration of ba1-igw-1 30

Figure 5 HW configuration of ba-six-1 30

Figure 6 HW configuration of ba1-p-1 and ba2-p-2 32

Figure 7 HW Configuration of ba2-pe-4 34

Figure 8 HW Configuration of ba1-pe-5 34

Figure 9 HW Configuration of ba1-pe-6 and ba1-pe-7 36

Figure 10 Architecture of CO BB 39

Figure 11 HW configuration of bb1-p-1 40

Figure 12 HW configuration of bb2-p-2 40

Figure 13 HW configuration of bb1-pe-1 41

Figure 14 HW Configuration of bb2-pe-2 41

Figure 15 HW Configuration of bb1-cat-1 and bb1-cat-2 42

Figure 16 Architecture of CO KE 43

Figure 17 HW configuration of ke1-p-1 44

Figure 18 HW configuration of ke2-p-2 44

Figure 19 HW Configuration of ke1-pe-1 45

Figure 20 HW Configuration of ke2-pe-2 45

Figure 21 HW Configuration of ke1-cat-1 and ke1-cat-246

Figure 22 New Architecture of Regional PoPs (10k based) 48

Figure 23 New Architecture of regional PoPs (7206VXR based) 48

Figure 24 HW Configuration of 10008 in Regional PoPs (ZA, NI, TT, PO) 49

Figure 25 HW Configuration of 10005 in Regional PoP Trencin (TN) 49

Figure 26 HW Configuration of 7206VXRs in Regional PoP 50

Figure 27 OSPF enabled links 54

Figure 5 Layer 2 Frame with 2 MPLS Labels 60

Figure 6 MP-BGP VPN Route Distribution example 63

Figure 8 VPN route distribution using partitioned RRs 64

12

Figures

Figure 10 Route Reflector Redundancy in the <Customer Name> Networks 65

Figure 12 Redundant Route Reflectors with same cluster-id. 67

Figure 13 Unique RD per each VPN 71

Figure 14 Unique RD per site for each VPN 73

Figure 18 PE-CE eBGP with unique AS 79

Figure 20 PE-CE eBGP with single network wide AS 80

Figure 48 Internet Access from a VPN using separate CEs 84

Figure 49 Internet Access from a VPN – Single CE (two links in CEred, single link on CEblue) 86

Figure 50 NAT in CE router 88

Figure 1 - Traffic Engineering Mechanisms 91

Figure 2 - Traffic Engineering Path Setup 94

Figure 3 - TE FRR Example 96

Figure 4 - Topology Without Tunnels 99

Figure 5 - R1 Routing Table – No MPLS TE 100

Figure 6 – Topology With TE Tunnels 100

Figure 7 - R1 Routing Table With Autoroute Announce 100

Figure 8 - Forwarding Adjacency Topology 101

Figure 9 - "3" Core Network Architecture 106

Figure 10 - Illustration of Primary and Backup TE Tunnels 107

Figure 51 Various interpretations of the TOS field 114

Figure 52 DSCP Interpretation 117

Figure 53 Adaptive jitter buffer 120

Figure 54 - Call admission control 120

Figure 55 LFI to reduce frame delay and jitter 121

Figure 56 Overview of end-to-end delay segments. 123

Figure 57 DSCP to EXP mapping 124

Figure 58 DSCP / MPLS Headers 124

Figure 59 QoS mechanisms overview 126

Figure 60 In/Out-contract Marking and Policing (example for Business class) 130

Figure 61 CAR based In/Out-contract Marking and Policing 131

Figure 62 WRED Algorithm 136

Document Control

Authors:

Change Authority:

Reference Number: EDCS-xxxx

HistoryTable 1 Revision History

Version No.

Issue Date Status Reason for Change

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Document Control

ReviewTable 2 Revision Review

Reviewer’s Details Version No. Date

<Name>

<Organisation>

<Version number> <dd-mmm-yyyy>

Change Forecast: Medium

This document will be kept under revision control.

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Document Control

Design AcceptanceThe signatories below confirm that the design meets the requirements specified. The design is subject to change during or following staging.

CISCO SYSTEMS Slovak Telecom

By:__________________________________ By:_____________________________________

Name: Name:

Title: Title:

Date:________________________________ Date:___________________________________

About This Design Document

Document PurposeThe purpose of this document is to outline the Cisco Systems recommended Low Level Design (LLD) for <Company’s name and Project Name>. It details the physical and logical requirements and how we will accomplish these requirements.

The document is split into following main sections,

Current Architecture and Network Design

Planned Services

Proposed Design and Architecture

OSS

Note: The above sections may change depending on the customer’s needs

The document provides sufficient detail to derive the device configurations that will be documented in the Network Implementation Plan. Some parameters may be determined during network deployment.

ScopePlease refer to Statement of Work documents for exact definition of project deliverables.

Document Usage GuidelinesThe document should be used as a guideline for deriving the necessary information to ultimately create the configurations that allow the network to provide the necessary services. The more theoretical sections should be used in conjunction with the practical sections in order to allow the deployment engineer to understand the service requirements behind the configurations. This will also allow the deployment engineer to take certain decisions when deploying and configuring the network.

As long as the Low Level Design document is in a draft format, it is susceptible to modifications and additions initiated by Cisco Systems or by the customer.

After acceptance of the LLD by the customer, the LLD document is still a living document that will be updated by experiences gained throughout the deployment and testing phases.

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About This Design Document

Assumptions and Caveats

Based on the input from CRDR ,HLD,SOW and Site Survey write down the necessary assumptions and caveats

It is assumed the reader is familiar with the <Customer Name> service requirements. Furthermore it is also assumed the reader is familiar with Cisco IOS and has a basic understanding of the network and technologies that will be used to fulfil the customer requirements.

Related DocumentsWrite down the links to CRD, CRDR, SOW, HLD and Site Survey

Network Overview

Describe what kind of customer and their core business. Also at a high level explain their current architecture with more details in the following section. This information can be collected from CRD and HLD

Network Topology

WAN Overview

The following figure is provided for illustrative purposes and depicts a high-level view of <Company’s name> network. Picture is simplified for easier understanding of WAN network topology.

Figure 1 <Company’s name> network – WAN topology

Network Infrastructure

Core

If possible provide the details of current core network. The platforms used, kind of links, what routing protocol etc.

Edge

The following types of devices are installed in <Company’s name> network as Provider Edge (PE) routers:

Access

Customer Edge (CE) routers are classical IPv4 routers and will interconnect customer sites with PE routers via leased lines (as described in Error: Reference source not found chapter below). CE routers usually reside in customer premises. CE router can be managed by <Company’s name> or by the customer.

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Traffic Flow and CharacteristicIn this section explainand characterize the custoemnr traffic. Explain the load that major pops(or even links) are carrying. What additional traffic is expected with the new deployment.

Existing Services and SLAsIn this section explain the current services that the customer is offering and the SLAs ,if any , associated with these services

Proposed Network Architecture

In this chapter we highlight the architecture that is being proposed for the customer based on the requirements listed in the CRD. Following chapter would go into the details of how this architecture would be deployed.

Design ConsiderationsThis chapter summarizes the design objectives that have been followed throughout the LLD, and the design rules we have taken to meet these objectives.. Following are the list of these objectives as dictated by the customer

MPLS Network Architecture

Following are just some of the examples. Customize this section based on your customer requirements

Fast convergenceFast convergence and network stability are two orthogonal components in any network design. Accurately measuring and interpreting the convergence time in complex topologies is somewhat like rocket science as many factors are involved. Improving the overall convergency by tuning the relevant parameters is a complex task that requires in depth analysis of all side effects (e.g. CPU utilization). We recommend to tune the convergence of routing protocols in a separate project. The scope of this project should be exclusively the optimization of convergency in ST MPLS network, by introducing new features (e.g. Traffic Engineering Fast Reroute) and tuning of routing protocol timers (see OSPF Convergence chapter)

Network Stability and ScalabilityAny routing protocol would scale well, if the routing information is stable. Stability of backbone IGP was one of the main concerns in the former ST network. For this reason the following changes have been made during previous project phases :

o Offload of any customer routes from backbone OSPF into BGP.

o Subnet aggregation of unstable leased-line connections and redistribution as static route into BGP.

o Subnet aggregation the of dial-up customers with fixed addresses on VPDN tunnel concentrator, and redistribution as static routes into BGP

Network resilienceST MPLS network has been designed for high availability. Physical and logical design ensures that primary and backup path exists between any two core routers. Core routers are equipped with primary

21

and backup route processors. Resilient connections between regional PoPs and Core locations will be rolled out in project phase 8A.

Network securityCisco has implemented best-practices security mechanisms on ST routers to protect the network. Customer security and managed firewall service was not in the scope of any Cisco project.

SimplicityST MPLS network design is clean and simple to understand. Any feature or design element that would increase network complexity - but have a limited overall benefit - has been avoided. ST has decided to clean-up the existing IP addressing scheme and migrate from multi-area OSPF into single-area design.

MPLSLDP has been chosen for label distribution in ST MPLS network. LDP is enabled on all core links (P-P, P-PE, P-RR, P-iGW).

Quality-of-Service

Traffic prioritisationThe following Classes of Service are implemented in the <Customer Network> network: Voice, Streaming, Business, Standard. Each class has different QoS attributes and guaranteed (configured) bandwidth that cannot be utilised by any other class during congestion periods.

Backbone links must be provisioned with sufficient capacity for each of the classes!

FlexibilityModular QoS CLI allows to map traffic flows of <Customer Name> customers in one of the Classes of Service. Such classification and marking is extremely flexible (different customers can map different applications in any of the classes), but requires the understanding of traffic profiles (e.g. SMTP or any other data traffic must not be mixed with delay-sensitive VoIP packets).

Scaleable implementationThe customer-specific QoS configuration is implemented on CE routers – QoS configuration template on PE and P devices will remain stable and the same for all ST customers. VPNSC shall be used for accurate provisioning of QoS parameters on access (PE-CE) connections.

MPLS/VPN Services

Flexible and scalable managed IP VPN serviceAchieved through MPLS technology, properly applied MPLS/VPN functionality and VPNSC management system1.

Service resilienceResilient MPLS backbone, redundant route reflectors and the possibility of fully resilient connectivity scenarios on access-layer (2CE-2PE) in all PoPs, are necessary building blocks for high availability MPLS/VPN service.

End-to-end Quality of ServiceAchieved through the use of various Diffserv mechanisms: classification, marking, policing, queuing and dropping. QoS is implemented on access layer and in the backbone.

1 VPNSC and NMS design is covered in separate LLD document.

22

Internet Access for MPLS/VPN customers Internet access from the MPLS/VPN is provided for customers with such requirement. For security reasons we only recommend to implement the Internet connection through a dedicated CE router and dedicated access-layer circuit (see chapter for detailed description)

SecurityAssuming that MPLS core is secure, the MPLS/VPN solution offers same level of security as the traditional layer-2 VPN networks.

Detailed Naming and Addressing Specifications

BGP AS Number

AS number for <Customer Name> MPLS network and inter-domain routing is <AS number>

<Customer Name> Routers

Naming convention for backbone routers has been defined by <Customer Name> as part of current deployment.

Explain in detail the nomenclature used by the customer or will be used by the customer

Customer Edge (CE) Routers

Naming convention for CE routers shall in addition to backbone naming scheme incorporate the customer name or customer ID.

DNS domain name

The domain name for <Customer Name> networking equipment shall be <domain name>

IP Addressing

Explain in detail the IP addressing scheme in customer’s network

Loopbacks

The following address block is used for numbering of Loopback02 interfaces in <Customer Name> MPLS network:

X.X.X.X.

Give any additional details as it relates to loopback addresses

2 Loopback interfaces are used primarily for OSPF stability, creation of iBGP and LDP neighborships.

23

Backbone Links

Backbone connections are numbered with IP addresses from the following subnets:

X.X.X.X

Explain in detail how these subnets would be allocated to different links

Existing Routers

In this section explain any renumbering of ip addresses that might be needed for any existing infrastructure

MPLS/VPN Access Connections

<Customer Name> has allocated the address pool

x.x.x.x/y

for numbering of MPLS/VPN access connections.

Internet Access Connections

<Customer Name> has allocated the following address pool for numbering of access connections for Internet customers:

x.x.x.x/y

IP-SLA

Depending on how IP-SLA is deployed , explain addressing scheme that would be required

MPLS/VPN Attributes

VPN naming and addressing is described by four attributes. These are the VRF name, RD, RT and SOO. Detailed naming of MPLS/VPN attributes are given in the NMS document (see Error: Reference source notfound)

VRF Name

The VRF name is locally significant on the PE router. Service providers that provision the MPLS/VPNs manually (via CLI on router console) are advised to use a VRF name that is recognisable across the whole network in order to aid troubleshooting. The name should identify the predominant function of the CEs connected to the VRF, this can be a word to identify the customer or, in the case of a VRF that is shared by multiple customers, the type of service offered by the attached CEs.

24

Explain how VRF name would be configured. Also explain if any provisioning tool like ISC is being used

RD

Explain how RD is being assigned. Also explain if any provisioning tool like ISC is being used

RT

RTs define the VPNs, the value is therefore significant across the whole network. A different RT is required for each VPN, hub-and-spoke VPNs can be considered as 2 uni-directional VPNs and therefore need 2 RTs if bi-directional routing is required.

Explain how RT is being assigned. Also explain if any provisioning tool like ISC is being used

SOO

SOO is required in order to provide loop avoidance on multi-homed sites. The same SOO attribute should be added to every routing update originating on the multi-homed site. Routes received by a VRF carrying a SOO also exported by the VRF should be filtered out so that they are not imported. Only multi-homed sites require the SOO attribute so SOO values will only be allocated as required.

Explain how SOO is being assigned. Also explain if any provisioning tool like ISC is being used

BGP AS Numbers

When peering with a customer CE router, the customer can use his registered ASN if he possesses one. If not, private ASNs (64512 to 65535) can be used on the CEs.

The same ASN can be used for all the sites of a VPN to conserve the number of ASNs; this is recommended and also allows for VPNs that have more than 1024 sites. The “as-override” is used on the PEs in order to reuse the same ASN for all the sites.

25

Deployment Guidelines

In this chapter we’ll exaplain you how to deploy the architecture proposed in the previous chapter

Physical Network DesignThe content is this section is only for reference purpose. You need to add details specific to your own customers. This is confidential information In no way should this information be shared with non-cisco folks

Layer-2 Transport Media

The following summarizes the physical layer transport in ST MPLS network.

Inter-site connectivity

o POS STM-16 over DWDM is used to interconnect:Core COs BA, BB and KE 7304 SIX router and P router in BA.

o POS STM-1 over SDH interconnects regional PoPs (PEs) with core COs (Ps)

Intra-site connectivity

o Back-to-back POS STM-16 is used for connectivity between P and collocated IGW routers in BA PoP

o Back-to-back GE connections are deployed for the following device pairs: 10008 (PE) -12410 (P) ; Bratislava, Banska Bystrica, Kosice7600 (PE) -12410 (P) ; BratislavaERX (DSL) -12410 (P) ; Bratislava10008 (PE) -12012 (P) ; Banska Bystrica

o Back-to-back POS STM-1 is used for the following links: 12406 (iGW) -12008 (iGW) ; Bratislava (2 x STM-1) (PE) - (P) ; Any other collocated PEs in central offices 7204VXR (RR) -12xxx (P) ; BA & BB

o Switched FE connections are used to connect existing ST IP (CE, NAS) routers that are cascaded behind new PEs. Layer 2 switches (Cisco 4503/3550-24) are used for port aggregation.

26

Central Office Bratislava [BA]

The chapters below depict the architecture of the three central offices and a typical implementation of a regional PoP in ST MPLS network.

Central Office in Bratislava is a major hub in ST network, because of the largest concentration of customer base in that area. For this reason, ST decided to build the BA CO resiliently and with powerful routers. The devices in BA CO can be logically grouped into four layers: Peering, Core, Aggregation and Access.

Two Firesections

The Bratislava CO will be divided into two physically separated firesections (1 and 2). Main components of peering, core and aggregation layer will be deployed in different locations to achieve network resilience in case of a major disaster. Customers can be dualhomed to PE routers in both firesection in order to provide them a maximum of redundancy.

The architecture of BA CO is depicted on the following figure.

27

Figure 2 Architecture of CO BA

Peering Layer

Internet Gateway Routers (ba1-igw-1, ba2-igw-2)

Two routers (Cisco 12406 and Cisco 12008) will be installed in BA CO for IP connectivity between ST MPLS network and:

Downstream ISPs (eg. local ASP - Application Service Provider) that pay for transit service to ST – these are in fact customers of ST.

Upstream ISPs (eg. Deutsche Telekom, UTA) that provide global Internet reachability for customers of ST.

Each iGW will have a POS STM-16 back-to-back connection with a different P router. Interconnections with ISPs can be either POS STM-1 or E3 leased lines.

Both iGWs are equipped with powerful route processors (primary and redundant) that can handle large number of BGP sessions, and will have installed sufficient amount of memory to carry one or more copies of full Internet routing table.

Back-to-back links between iGW routers

28

Both iGWs will inject a BGP default route towards PE routers. A PE router will select the default route based on IGP distance to originating iGW, and eventually send all Internet traffic to the closest iGW. However, this iGW may not be the best exit point for a given Internet destination, so the packets would have to be re-routed to the neighbouring iGW to be delivered to the upstream ISP. For this reason, two POS STM-1 back-to-back links are installed between iGWs. No other traffic (eg. packets between two ST PoPs) are passing these two links.

An alternative solution would be to download full Internet routing table to any PE router, which can in turn deliver the Internet traffic to the right iGW. This would result in more optimal traffic flows across ST core, and enable “distributed” peering system, with possibility of connecting ISP circuits in any PoP. Assuming that BGP dampening is enabled on border routers, and number of routes that can be accepted from any ISP is limited3, the major drawback is memory requirements (min. 256 MB) on all PE routers due to large number of routes in the global Internet routing table.

Figure 3 HW configuration of ba2-igw-2

3 It is a good practice to define the maximum number of prefixes that can be accepted from any eBGP peer. This is for example to prevent the situation where a peering partner at SIX advertises the full Internet routes to ST.

4 x POS STM-1

1 x POS STM-16

8 x POS STM-1

6 x E3

GRP Redundant

GRP

CSC SFC

CSC

Alarm Alarm

SFC

SFC

Power Power

P router

Upstream/Downstream ISP

0

1

2

3

4

5

12406

-

29

Figure 4 HW configuration of ba1-igw-1

SIX Internet Gateway Router (ba-six-1)

One 7304 router (ba-six-1) is collocated at SIX premises, for mutual and free-of-charge exchange of customer traffic between peering partners at Slovak Exchange Point. ba-six-1 router is attached to the SIX switch with a GE interface, and interconnected with ST core router ba2-p-2 via a POS STM-16 connection.

Figure 5 HW configuration of ba-six-1

Resiliency in Peering Layer

It is recommended and a good decision to terminate at least one upstream ISP connection on each iGW. This will protect from failures on a single peering circuit, and/or major failure of a single peering router

-

-

--

1 x POS STM-16 P router

Peering partners @ SI X

4

2

0

5

3

1NSE100GE0 GE1

7304

4 x

PO

S S

TM

-1

- -

CS

C 0

CS

C 1

1 x

PO

S S

TM

-16

4 x

PO

S S

TM

-1

-

GR

P R

edu

ndan

t

GR

P

Pow

er

Pow

er

12

00

8

P router

Upstream/Downstream ISP

0 1 2 3 4 5 6 7

30

(either ST’s or the one of upstream ISP). Having two redundant Internet connections on separate routers will also permit software and hardware upgrades on iGWs without long downtimes.4

The two iGWs distribute BGP routes (default route and full Internet table if required) to other BGP neighbors in ST network via two redundant route reflectors.

The Internet connectivity scheme with physically separated IGW routers protects against the failure or major disaster in one of the Bratislava firesections. Internet connectivity will remain through the backup upstream ISP in the other firesection.

There’s currently a single router installed at SIX premises. If this router or a link between ba2-p-1 and SIX router fails, the direct connectivity with SIX participants will be lost. Nevertheless, this does not represent a single point of failure, because the peering partners’ networks can be during failure reached5 across upstream ISPs.

Core Layer

MPLS P Routers (ba1-p-1, ba2-p-2)

ST has selected two Cisco 12410 routers for MPLS P devices in Bratislava CO. These P routers do not perform any aggregation layer services (eg. termination of customer links, or peering circuits, BGP routing, etc.) P routers are also not routing the IP packets across ST core; the only6 task of P routers is to label switch the MPLS frames through high speed links, respecting the queuing and dropping attributes which are encoded in the EXP bits of MPLS labels.

Each P router links the following devices:

Remote P router - GSR. POS STM-16 links interconnect the P routers into a high-speed backbone. Underlying technology is DWDM.

Remote PE. Regional PEs in remote PoPs interconnect with P routers via POS STM-1 links.

Collocated PEs are attached with P routers either via a back-to-back POS interfaces, or using a GE technology in a back-to-back mode.

4 A short downtime will occur because of eBGP convergence throughout the Internet.5 Most likely this would introduce higher RTT and jitter, and increased load on generally very expensive transit connections with upstream ISPs.6 This is not entirely true because the locally sourced packets will be subject to label imposition (eg. OSPF updates)

31

Figure 6 HW configuration of ba1-p-1 and ba2-p-27

Resiliency in Core Layer

Dual triangle topology of ST core network is resistant to failures on a single P-P link. When a P-P link fails, or when a port on line card fails, the transit traffic between the two P routers can be rerouted across longer path around the core ring. This should not be very frequent event, also because of layer-2 resiliency built in DWDM ring. Nevertheless, a failure on P-P link has to be considered, because it would affect the cumulative backbone throughput and quality of MPLS/VPN services.

The ST core network is also protected against node failures in Bratislava, Banska Bystrica and Kosice. If one node fails, the traffic is rerouted across the second triangle.

The higher RTT and jitter because of increased number of hops is not questionable, because there’re currently only four P routers in the core ring, and they’re linked with high-speed 2.5 Gbps connections.

However, if the core links are well utilised (eg. 70-80%) during normal network operation (although that is not expected in ST MPLS network very soon), the failure on one P-P link might cause temporary congestions and packet loss on the alternate path. This can be dangerous if for example the SLAs of Business data class guarantee certain max. % of packet loss at any time. In this case the workaround

7 New four-port STM-16 LC will be installed in ba1-p-2 during Phase 8A Project. Three-port GE LCs will be replaced by new four-port Eng3 LCs. This will allow proper QoS implementation on P-PE connection (on GSR side).

4 x

PO

S S

TM

-16

4 x

PO

S S

TM

-16

-

4 x

GE

--C

SC

0

8 x

PO

S S

TM

-1

GR

P R

edun

dant

GR

P

4 x

GE

1 2 4 5 6 7 8 9

CS

C 1

SFC

1

SFC

2

SFC

3

SFC

4

Alr

m 0

Alr

m 1

SFC

0

Power Power12410

P, IGW and SIX router

RR, MPE, Regional PEs, 7513 PE router

Collocated PEs

0

P router

8 x

PO

S S

TM

-1

3

32

solution may be to overprovision the class bandwidth for Business data class, on account of under provisioned class bandwidth in Standard class.

Aggregation Layer

10008 MPLS PE - Concentration of Leased Line Customers (ba1-pe-5, ba2-pe-4)

Two ESR 10008 routers are installed in Bratislava CO for termination of leased-line customer connections (MPLS/VPN and Internet customers) and linking the non-upgraded regional PoPs of ST with MPLS core. For this, the 10008s are equipped with 24 E1 ports and 6 POS STM-1 ports.

The 10008 PEs are connected to P routers with two GE uplinks in a back-to-back mode, as shown on the following table. LX long haul GBICs connected via single mode dark fiber (10/9 micron) are used for longer distances (< 6,2miles/10 km) between firesections.

Table 3 PE-P Connectivity in CO BA

PE Device PE Name Primary P Backup P

ESR 10008 ba1-pe-5 ba1-p-1 ba2-p-2

ESR 10008 ba2-pe-4 ba2-p-2 ba1-p-1

7609 ba1-pe-6 ba1-p-1 ba2-p-2

7609 ba1-pe-7 ba1-p-1 ba2-p-2

33

Figure 7 HW Configuration of ba2-pe-48

Figure 8 HW Configuration of ba1-pe-59

8 New 10008 chassis with 6xPOS STM-1LC, 24xE1LC and two half-slot GE LCs will be installed in BA firesection 2. One 6xPOS STM-1 LC will be taken from current ba-pe-4 router. One 8xE3 LC will be taken from ke1-pe-1 router.9 One 8xE3 LC will be taken from bb1-pe-1 router.

24

xE1

-

PR

EB

PR

EA

6x

PO

SS

TM

-1

1 2 3 4 6

Pri

mary

PEM

Redun

dan

tPE

M1

00

08

Customers + Regional PoPs (CEs)

Backup P

Primary P +

6x

PO

SS

TM

-1

24

xE1

Backup P

1 x

GE

1 x

GE

87

-

5

8 x

E3

1x

GE

24

xE1

1x

GE

-

PR

EB

PR

EA

6x

PO

SS

TM

-1

1 2 3 4 6 7 8

Pri

mary

PEM

Redun

dan

tPE

M1

00

08


Backup P

Primary P

6x

PO

SS

TM

-1

24

xE1

5

8 x

E3

34

7609 MPLS PE - Collocation of Server Farms (ba1-pe-6, ba1-pe-7)

Two 7609 routers in Bratislava CO provide Internet connectivity for collocated server farms of ST customers. Moreover ST IP (CE, NAS) routers is directly connected via FE. Currently each 7609 is equipped with the following modules:

one 48 port 10/100 catalyst module

o with daughter Distributed Forwarding Card - DFC

one OSM 4-GE module

two supervisor SUP2 modules (primary and redundant) each with

o PFC2 and MFC2

o 2 x GE ports on MFC2 - these are active on redundant SUP2 too.

one Switch Fabric Module – SFM2

Each 7609 has a primary and backup GE uplink towards the P routers in BA PoP.

35

Figure 9 HW Configuration of ba1-pe-6 and ba1-pe-710

10008 / 7206VXR MPLS PE - Regional (remote) PoPs

The following regional PoPs are attached to Bratislava core PoP: Trnava, Nitra, Trencin, Senica, Topolcany, Trencin, Levice, Nove Zamky and Dunajska Streda.

Depending on the PoP location, there will be either one 10008 and one 7206VXR PE router installed, or two 7206VXR PE routers. Each regional PoP will be dualhomed to both P routers in Bratislava via POS STM-1 links.

Please find more details of a typical regional PoP architecture in chapter Regional PoPs

7206VXR - MP-BGP Route Reflectors

Two MP-BGP RRs are hosted in Bratislava CO. One 7204VXR IPv4 RR (ba1-irr-1) is connected with the collocated ba1-p-1 router with a single POS STM-1 interface. The other VPNv4 RR (ba2-vrr-2) is connected with the collocated ba2-p-2 router. There’s no need for redundant connection with a second P router, because the resiliency is achieved on BGP layer (two RRs).

10 New 16 port GE module will be installed in ba1-pe-6 and ba1-pe-7 durin Project Phase 8A

SFM

2 (

Sw

itch

Fabri

c M

odule

)

-

SU

P2 R

edu

n.

SU

P2

48

x 1

0/1

00 R

J-2

1(D

FC)

PSPS

Redundant7609

CE/NAS

Backup/Primary P

2 x

GE

2 x

GE

(PFC

2 +

MS

FC2

)

* Linecards only in slots 3, 4, 6-9

(PFC

2 +

MS

FC2

)

1235789

OS

M

4 x

GE

-

PIX Firewalls (BA Datacenter) + NAS (5850)

16

x G

ENAS (5850)

46

36

The 7204VXR RR will not forward any customer traffic.

75xx - BA-Border1, BA-Border2

The former BA-Border1 router in Bratislava PoP has been been upgraded to support MPLS/VPN technology. It is now used as PE device in new ST MPLS network (ba1-pe-2). The former BA-Border2 router has not sufficient hardware capabilities to support MPLS/VPN services. It will be used as CE router instead.

As per MPLS/VPN terminology, any remote PoP connected to ba1-pe-2, represents a MPLS/VPN CE router in the MPLS network.

Resiliency in Aggregation Layer

Since the core layer in centeral offices consists of two P routers, the aggregation layer routers will be resiliently connected with the rest of the ST network. When the port on P or PE router fails, or if the whole P router goes down, the traffic would be rerouted via backup PE-P uplink as per OSPF calculation.

If for any reason it is not possible to interconnect a PE router with both P devices, service resiliency can still be achieved on access layer: with two CE routers interconnecting with two PE routers via two separate connections.

Access Layer

Customer Edge – CE Routers

There are two type of CE routers connected to ST PE routers: customer managed and ST managed CE devices.

Cisco recommends to limit the number of various platforms and interfaces, in order to minimize operational and management costs. For example:

Low-end CE router: 800, 1700 and 2600 series

Mid-range CE router: 3600 series

High-capacity CE router: 7200 (or more powerful device when required)

Customer managed CE router can be any device, which supports the leased line technology and protocols offered by ST.

Existing ST IP Access Connections

In theory, ST could re-home all customer leased lines from CE routers to MPLS PEs, but this task is already a huge project, requires lots of coordination with customers.

A more elegant approach has been chosen by ST. The former distribution layer was cascaded behind the MPLS PEs, in order to leave hundreds of customers’ leased lines intact. In MPLS/VPN terminology, the old distribution layer routers have become CE devices; that’s why ST has renamed them tinto ‘CE’ routers.

37

The following routers in Bratislava PoP are connected with a single FE back-to-back connection to the 7609 PEs: ba2-ce-1, ba2-ce-2, ba2-ce-3, ba2-nas-1, ba2-nas-2.

New 5850 access servers will rolled out in a separate project. Two logical separated access servers (ba2-nas-3 and ba2-nas-4) on the same physical device will be installed in Bratislava firesection 2. They will be dualhomed to the 7609 PEs via two GE uplinks.

Alternative to migration of existing leased-line customers

ST could progressively turn the old IP routers into MPLS PEs and attach them directly to P routers. For this, the old 7206 and 3640 routers shall be SW upgraded with a more recent (and stable) IOS release, which offers required MPLS/QoS functionality on given hardware.

Assuming that CPU utilisation on existing CE routers is not problematic, this might be a more appropriate alternative than migration of hundreds of leased lines to the new platforms.

Resiliency in Access Layer

Having two PE routers in each regional PoP, and two resilient connections between regional and core PoP provides the possibility to dualhome access devices to both PE routers. Redundant L2 access switches in core PoPs Banska Bystrica and Kosice (4503) and regional PoPs (3550-24) are used to aggregate FE connections from access devices.

38

Central Office Banska Bystrica [BB]

New 12410 P and 10008 PE router will be installed in a separate location (firesection) in Banska Bystrica. The currently installed 10005 router will be moved to regional PoP Trencin, while the existing 10008 router remains in the current location.

New 4503 aggregation switches will be deployed in one firesection to connect existing ST IP devices and new customers via FE. ST IP devices will be dualhomed to switches via back-to-back FE links, in cases where additional LAN interfaces are available (e.g. NAS).

The architecture of CO BB is depicted on the following figure.

Figure 10 Architecture of CO BB

Core

Aggre

gati

on

bb2-vrr-27204VXR

bb2-p-212410ba2-p-2

ke2-p-2

Aggre

gati

on

Acc

ess

bb-ce-17206

bb1-pe-37507

Core

bb1-p-112012

bb1-irr-17204VXR

7 x7 x

ba1-p-1

ke1-p-1

limi-pe-1

prie-pe-1

povb-pe-1

za-pe-1

mart-pe-1

bb-nas-15800

bb-nas-25800

bb-saa-22620XM

bb-ce-23640

bb-saa-12620XM

bb1-cat-14503

bb1-cat-24503

bb2-pe-210008

bb1-pe-110008

Ethernet

BB CO Firesection 2 (Horna 77)

BB CO Firesection 1 (Skolska 10) POS STM-16

POS STM-1

GigabitEthernet

FastEthernet

Serial

limi-pe-2

prie-pe-2

povb-pe-2

za-pe-2

mart-pe-2

lucn-pe-1zvol-pe-1

lucn-pe-2zvol-pe-2

39

Figure 11 HW configuration of bb1-p-111

Figure 12 HW configuration of bb2-p-212

11 New 1 port STM-16 and 4 port GE LC will be installed in bb1-p-1 during Phase 8A Project. 1xGE LC will be removed12 New installed during Phase 8A Project

---

CS

C 0

16

x P

OS

STM

-1

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GE

1 2 3 4 5 8 9

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C 1

SFC

1

SFC

2

SFC

3

SFC

4

Alr

m 0

Alr

m 1

SFC

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Power Power12410

P routers

Regional PEs, 7507 PE router

BB Aggregation

4 x

PO

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TM

-16

0 1

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Power A Power B12012[BB]

P router

Regional PEs

BB Aggregation

11

12

1

1 x

PO

S S

TM

-16

10

4 x

GE

- -

40

Figure 13 HW configuration of bb1-pe-113

Figure 14 HW Configuration of bb2-pe-214

13 Two new half-slot and one single GE LC will be installed in bb1-pe-1 during Phase 8A Project. The second single slot GE LC will be moved from existing 10005 to bb1-pe-1. One 8x E3 LC moved to ba1-pe-5 router.14 New 10008 will replace existing 10005 (moved to Trencin) during Phase 8A Project

1 x

GE

-

PR

E B

PR

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S S

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-1

1 6 7 8

Pri

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MR

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00

8


Primary P + Backup P

24 x

E1

3 5

24

x E

1

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GE

-

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GE

2

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GE

ST IP devices (CAR, Dist) via 4503

8 x

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24

x E

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Primary P


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E3

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7

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GE

1 x

GE

65

-

41

Figure 15 HW Configuration of bb1-cat-1 and bb1-cat-215

15 New installed during Phase 8A Project

1

4503

SUP IV 2 x GE

2 6 x GE

3 48 x FE ST IP devices (CAR, Dist)

GE Uplinks to PEs and other Cats

42

Central Office Kosice [KE]

New 12410 P and 10008 PE router will be installed in a separate location (firesection) in Kosice. ST IP devices will be migrated to new installed 4003 aggregation switch in current location. Another switch will be installed in the new location (firesection 2). Both switches will be dualhomed to 10008 PE routers via GE uplinks.

The architecture of CO KE is depicted on the following figure:

Figure 16 Architecture of CO KE

Core

Aggre

gati

on

ke2-p-212410ba2-p-2

bb2-p-2

Aggre

gati

on

Acc

ess

ke-ce-17206

ke1-pe-37507

Core

ke1-p-112012

7 x7 x

ba1-p-1

bb1-p-1

hume-pe-1

snvs-pe-1

pp-pe-1

rozn-pe-1

mich-pe-1

ke-nas-15800

ke-nas-25800

ke-saa-22620XM

ke-ce-23640

ke-saa-12620XM

ke1-cat-24503

ke1-cat-14503

ke2-pe-210008

ke1-pe-110008

Ethernet

KE PoP Firesection 2 (Postova 18)

KE PoP Firesection 1 (Polska 4) POS STM-16

POS STM-1

GigabitEthernet

FastEthernet

Serial

bard-pe-1

po-pe-1

hume-pe-2

snvs-pe-2

pp-pe-2

rozn-pe-2

mich-pe-2

bard-pe-2

po-pe-2

43

Figure 17 HW configuration of ke1-p-116

Figure 18 HW configuration of ke2-p-217

16 New 1 port STM-16 and 4 port GE LC will be installed in ke1-p-1 during Phase 8A Project17 New installed during Phase 8A Project

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Figure 19 HW Configuration of ke1-pe-118

Figure 20 HW Configuration of ke2-pe-219

18 Four new half-slot GE LCs will be installed in ke1-pe-1 during Phase 8A Project. One 8x E3 LC moved to ba2-pe-4. 19 New installed during Phase 8A Project

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Figure 21 HW Configuration of ke1-cat-1 and ke1-cat-220

20 New installed during Phase 8A Project

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Regional PoPs

During transition phase of ST IP network to MPLS/VPN technology, the old 7206 (CAR/POP), 3640 (CAR) and AS5300 (NAS) routers have been cascaded behind 7206VXRs as CE devices. Each 7206VXR router have been attached with a single POS STM-1 uplink to the closest P router.

In the scope of phase-2 of MPLS/VPN project (deployment of 17 new PoPs) ST decided to improve the design of remote PoPs. The design change introduces a new Catalyst 3550 that will aggregate local LAN-attached devices. This will allow direct attachment of old STIP routers to the new PE router.

Connection between a Catalyst and PE router will be configured with encapsulation dot1Q and several logical sub-interfaces on PE router. Each sub-interface can be assigned to a different VRF, or to the global routing table, which makes deployment of co-located CEs or customers’ web servers straightforward. Number of VLANs in the Catalyst switch will correspond to number of VRFs implemented on the PE router (+1 for global RT).

Part of Project Phase 8A is to achieve higher service availability in the regional PoPs by deploying second PE routers.

Two groups of Regional PoP will be deployed:

A new C10k PE router will be implemented next to the current C7206VXR in 5 PoPs:(Zilina, Nitra, Trnava, Presov, Trencin)

A new 7206VXR will be implemented next to the current C7206VXR in 17 PoPs: (Senica, Topolcany, Dunjaska Streda, Nove Zamky, Prividza, Martin, Provazska Bystrica, Liptovsky Mikulas, Levice,Spisska Nova Ves, Bardejov, Poprad, Humenne, Michalovce, Roznava,Lucenec, Zvolen)

The following drawing shows the new design for the remote PoPs where a new 10k PE router will be deployed; Nitra PoP has been taken as a typical example.

Note: The new regional PoP design is described in Appendix II

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Figure 22 New Architecture of Regional PoPs (10k based)

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The following drawing shows the new design for the remote PoPs where a new 7206VXR PE router will be deployed; Senica PoP has been taken as a typical example.

Figure 23 New Architecture of regional PoPs (7206VXR based)

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Figure 24 HW Configuration of 10008 in Regional PoPs (ZA, NI, TT, PO)21

Figure 25 HW Configuration of 10005 in Regional PoP Trencin (TN)22

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21 New installed during Phase 8A Project22 Two new half-slot GE LCs will be installed in tn-pe-2 (moved from BB PoP) during Phase 8A Project

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Hardware/Software Release Table

The following table summarizes the IOS releases for different platforms in ST MPLS network.

Table 4 Software Release Table

Device Role in ST MPLS network IOS release Image Name

12xxx-GRP existing P, iGW12.0(25)S2

gsr-p-mz.120-25.S2

12xxx-PRP new P c12kprp-p-mz,120-25.S2

1000x PE 12.0(25)S1 c10k-p10-mz.12.0-25.S1

7609 PE <tbd> <tbd>

7304 SIX <tbd> <tbd>

7204VXR RR 12.0(25)S2 c7200-p-mz.120-25.S2

7206VXR PE 12.1(11b)E12 c7200-p-mz.12.1-11b.E12

2620XM SAA 12.2(8)T5 c2600-is-mz.122-8.T5

4503 Aggregation Switch 12.1(19)EW1 cat4000-i9s-mz.121-19.EW1

3550-24 Aggregation Switch 12.1(9)EA1c cc3550-i9q3l2-mz.121-9.EA1c

New Engine 3-based 4 port GigE linecards (4GE-SFP-LC, aka “Tetra”) will be implemented in 12012 and 12410 P routers in central offices. An IOS upgrade to 12.0(25)S is required to support this new hardware. 12.0(25)S is the first release supporting this new linecard.

Apart from the new hardware, which is the main factor for the IOS upgrade, some of the IOS releases in ST's network are vulnerable to Denial of Service (DoS) attacks. Refer to the following URL for more information : http://www.cisco.com/warp/public/707/cisco-sa-20030717-blocked.shtml

The core release 12.0(25)S2 is the third maintenance release of 12.0(25)S and should be deployed after as much as possible testing (during staging phase) on all 12xxx core routers and 7204VXR routers (acting as BGP RRs). Due to IOS bug CSCec57264, the 12.0(25)S2 release is not avilable for 1000x routers (already running 12.0(25)S1). 1000x routers should be upgraded to a later maintenance release of 12.0(26)S.

The new edge release 12.1(11b)E12 includes several bug fixes compared to the currently used 12.1(11b)E4b. It should be deployed on 7206VXR PE routers in order to improve stability and to fix vulnerability.

Once satisfied, the next step should be to deploy the code on one or two devices in a redundant and non-critical area of the network for one week pilot phase. During this period, ST should monitor the status of these devices to insure successful deployment The code should then be rolled out in a controlled and logical fashion.

From a strategic standpoint, Cisco recommends to use as few different IOS releases as possible. Using just one IOS release across all platforms is sometimes not achievable, due to the differences in HW architecture and feature requirements. Nevertheless, deploying 12.0(25)S2 on two platforms will be a first step towards the limitation of different IOS releases in ST’s network.

In the medium term (3 to 6 months from now), Cisco recommends to do a new IOS evaluation. The aim of this evaluation should be the definition of a long-term IOS strategy for ST’s network. The IOS strategy

http://www.cisco.com/warp/public/707/cisco-sa-20030717-blocked.shtml

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highly depends on the network evolution concerning new features and hardware deployments. Therefore it should be covered by ongoing Cisco Network Optimization Support (NOS).

Logical Network Design

IGP Routing – (OSPF or ISIS)OSPF is a link state routing protocol. It is called as such because it sends link states advertisement (LSA) to all the routers within the same hierarchical area. All the OSPF routing information is passed within these LSAs. After the routers receive that information they run the SPF algorithm to calculate the shortest path to each destination.

When an SPF router powers up all the routing protocol data structures are initialised and then the process waits for the interfaces to be functional. Once the interfaces are functioning the devices use the OSPF hello protocol to establish neighbourships. Once the hello exchange has finished and the neighbourship is established, hello packets are used as keepalives to identify which devices are active. When the link state databases of two neighbours are synchronised, they are said to be adjacent. Distribution of routing information is only performed between adjacent routers.

Each router sends periodically LSAs and also when a router's state changes. The OSPF database contents are compared with the received LSAs to identify possible topology changes.

The following is the generic OSPF router configuration.

!router ospf 1 log-adjacency-changes passive-interface Loopback0 network x.x.x.x y.y.y.y area 0!

The Role of OSPF in <Customer name> MPLS network

The <Customer name> MPLS network requires an underlying Interior Gateway Protocol (IGP) to be enabled for the following reasons:

BGP next-hop reachability.

Fast convergence after failure of backbone node or core link.

Shortest path routing across <Customer name> backbone.

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<Customer name> is already running OSPF in its current network. Therefore <Customer name> is very familiar with OSPF operation, and has gained lots of experiences in OSPF troubleshooting. <Customer name> has therefore requested to preserve the OSPF as IGP in current MPLS network. The choice of OSPF is a very good one as it is standardised, scales well and converges quickly.

OSPF is responsible for interior routing only ! It is not used to carry any customer addresses or linksNetwork addresses of the following links are carried in the OSPF LSAs:

backbone P-P links

distribution layer PE-P links

loopback0 interfaces

RR-P links

CE, NAS connections*

Figure 27 OSPF enabled links

In addition to backbone links, the subnets allocated to NMS VLANs and VPNSC LAN are redistributed in the backbone OSPF as connected/static routes. This is required to establish connectivity between NOC sites and P routers, which do not run BGP. <Use the above paragraph if you are not using an out of band connection for management purposes>

OSPF Areas

Single area or Multiarea OSPF would be implemented in the <Customer Network> network. This decision is based on:

Give reasons here. Also discuss in this sections how you are going to number OSPF areas

Discuss in detail the max number of routers that would there in an area. Talk about the scale numbers of ABRs, ASBRs

CAR3640

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OSPF Authentication

It is possible to authenticate the OSPF packets such that routers can participate in routing domains based on predefined passwords. By default, a router uses a Null authentication, which means that routing exchanges over a network are not authenticated. Two other authentication methods exist: Simple password authentication and Message Digest authentication (md5). Authentication does not need to be set, but we strongly recommended for security purposes. And we are recommending MD5 as the authentication method since it is provided higher security than plain text authentication method.

Message Digest Authentication is a cryptographic authentication. A key (password) and key-id are configured on each router. The router uses an algorithm based on the OSPF packet, the key, and the key-id to generate a “message digest” that gets appended to the packet. Unlike the simple authentication, the key is not exchanged over the wire. A non-decreasing sequence number is also included in each OSPF packet to protect against replay attacks.

This method also allows for uninterrupted transitions between keys. This is helpful for administrators who wish to change the OSPF password without disrupting communication. If an interface is configured with a new key, the router will send multiple copies of the same packet, each authenticated by different keys. The router will stop sending duplicate packets once it detects that all of its neighbors have adopted the new key. Following are the commands used for message digest authentication:

interface <interface type-number> ip ospf message-digest-key keyid md5 <key>

Router ospf 19 area <area-id> authentication message-digest

Loopback Addresses

Each of the OSPF speakers has a Loopback address configured. These are used to force stability of the routers OSPF ID. These loopback addresses are in OSPF passive mode to optimise the routing process.

OSPF Area Summarization

Discuss the details of summarization plans if any

OSPF Costs

Discuss here the costs of ospf for different links. Expalin any considerations kept in mind when deciding ospf costs. Following table can be used to define the costs

Table 5 Proposed OSPF Metrics

Bandwidth [Mbps] CE-PE

PE-PE

(none MPLS)

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iGW1-iGW2

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iGWx-P

PE-P backup

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E1 2 31300 - - -

E3 34 31200 - - -

FE 100 31100 - 5700 10700

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STM-1 155 31000 600 5600 10600

STM-4 622 30900 500 5500 10500

GE 1000 30800 400 5400 10400

STM-16 2500 - 300 5300 10300

STM-64 10 [Gbps] - 200 5200 10200

STM-256 40 [Gbps] - 100 5100 10100

Designated and Backup Designated Routers

On a multi-access media such as Ethernet it is a good idea to force the designated router and backup designated router to be routers that have more memory and greater processing power than the other routers in the area. Under the default election scheme, each router has the default priority of 1, therefore the router with the highest router id (i.e. Loopback IP address) becomes the designated router for the segment.

It is not mandatory to enforce the DR selection on multi-access media segments with just two OSPF speakers (e.g. GigE PE-P uplinks). Therefore these kind of Fast/Gigabit Ethernet interfaces in <Customer Network> network are defined as OSPF point-to-point links to prevent election of DR/BDR routers.

interface G 5/0 ip ospf network point-to-point

Default RoutesIf there are any default routes then explain how and where are they being injected

OSPF Convergence

Resiliency and redundancy to circuit failure is provided by the convergence capabilities of OSPF at layer 3. There are two components to OSPF routing convergence: detection of topology changes and recalculation of routes.

Detection of topology changes is supported in two ways by OSPF. The first, and quickest, is a failure or change of status on the physical interface, such as Loss of Carrier. The second is a timeout of the OSPF hello timer. An OSPF neighbor is deemed to have failed if the time to wait for a hello packet exceeds the dead timer, which defaults to four times the value of the hello timer. On a Serial, Fast Ethernet or Gigabit Ethernet interface, the default hello timer is set to 10 seconds; therefore the dead timer is 40 seconds

Recalculation of routes is done by each router after a failure has been detected. A link-state advertisement (LSA) is sent to all routers in the OSPF area to signal a change in topology. This causes all routers to recalculate all of their routes using the Djikstra (SPF) algorithm. This is a CPU intensive task, and a large network, with unreliable links, could cause a CPU overload.

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When link goes down and if layer2 is not able to detect the failure, convergence in the core can be improved by decreasing the value of the hello timer. The timer should not be set too low as this may cause phantom failures, hence unnecessary topology recalculations.

Remember that these timers are used to detect failures that are not at the physical level. For example, carrier still exists but there is some sort of failure in the intermediate network.

Once a topology change has been detected, LSA is generated and flooded to rest of the devices in the network. Recalculation of the routes will not occur until the spf timer has expired. The default value of this timer is 5 seconds. An spf hold time is also used to delay consecutive SPF calculations (give the router some breathing space). The default for this value is 10 seconds. As a result, the min time for the routes to converge in case of failure is always going to be more than 5 secs unless the SPF timers are tuned using OSPF throttle timers. As a result, it is now possible to schedule spf run right after flooding the LSA information but this can potentially cause the instabilities in the network e.g. even a flash congestion in the network for a very short duration could trigger declare the link down and trigger the SPF run.

These timers will be left alone in the initial implementation especially because in the next phase of this project, MPLS Traffic Engineering with Fast-ReRoute (FRR) capability will be deployed. Once FRR is implemented, tweaking OSPF timers become less of a concern.

A keepalive timer is also associated with the interface that will detect failure at a level lower that OSPF. The default for this timer is 10 seconds; again this will be left as default initially.

In the initial deployment of the Core network, all timers will be left at their default values as shown below. These could be slowly lowered and behavior of the network monitored if faster convergence is required.

If the timers are not default then explain why they are being changed and also the values used and configurations

Discuss in detail the scaling issues. For example what are the max number of prefixes that can converge in a given time. Any other related work that may have been documented in DIG from SPSE or from inhouse testing of the architecture

Table 6 OSPF Timer Default Values

Timer Default Value

ip ospf dead-interval 4 x hello interval (40 sec)

ip ospf hello-interval 10 sec

ip ospf retransmit-interval 5 sec

ip ospf transmit-delay 1 sec

timers throttle spf <spf-start> <spf-hold> <spf-max-wait> 5000 msec 10000msec 10000msec

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OSPF DNS Lookup

A global configuration command “ip ospf name-lookup” would cause the router to look up the Domain Name System (DNS) names for all OSPF show commands, making it easier to identify devices.

vallentin#sh ip ospf nei

Neighbor ID Pri State Dead Time Address Interfacenice 1 FULL/DR 00:00:37 10.0.4.6 Ethernet0/0lisjak 1 FULL/ - 00:00:30 10.0.4.2 Serial5/0

However, this may result in slow response of various show commands, because of slow response times on DNS queries. <Customer name> Operations team or Cisco’s deployment team should enable OSPF name-lookup on a few routers initially, and observe the responsiveness of DNS system.

OSPF Configuration Template

The following generic OSPF configuration could be used on every router in the <Customer Name> network – just the router-id and hostname needs to be changed.

hostname <insert hostname>!interface Loopback0 ip address <address> <mask> no ip directed-broadcast!interface pos0/0 description <insert appropriate descriptor>ip address <address> <mask> ip ospf network point-to-point ip ospf message-digest-key 1 md5 <Change Me>!interface GigabitEthernet1/0 description <insert appropriate descriptor>ip address <address> <mask> ip ospf network point-to-point ip ospf message-digest-key 1 md5 <Change Me>

router ospf 100 router-id <lo0 address> log-adjacency-changes passive-interface Loopback0 auto-cost reference-bandwidth 10000 area 0 authentication message-digest network statements for loopback and core link addresses

OSPF Deployment Recommendations Summary for the <CUSTOMER NAME> network

List down any additional recommendations for ospf and try to summarize the main points

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Backbone Routing and Label Distribution ProtocolsThe three protocols are required in the core to provide a functional MPLS network include OSPF, LDP, and MP-BGP. OSPF provides IP Connectivity amongst the various end points and has already been discussed in the previous section. LDP is needed to distribute the necessary label information required to establish the label switched paths between the PE routers. MPLS in general, depends on IGP or in this case OSPF along with Cisco Express Forwarding to create the necessary forwarding table. CEF, LDP, and MP-BGP will be explored in greater detail in this section. Lastly, MP-BGP is needed to exchange the VPN routing information between VPN customer sites. On the PE routers, VPN Customer routes are kept in separate routing tables, known as VPN Routing and Forwarding tables (VRFs). Routes in the global routing table are not reachable by routes in VRFs or vice versa.

Cisco Express Forwarding (CEF) Switching

Cisco Express Forwarding (CEF) is advanced Layer 3 IP switching technology. CEF optimises network performance and scalability for networks with large and dynamic traffic patterns by essentially distilling the routing information into a forwarding database known as the FIB, Forwarding Information Database. Cisco Express Forwarding or CEF switching is a pre-requisite for MPLS to function properly. Therefore CEF must be configured on all the PE and P devices in the <CUSTOMER NAME> networks.

By default CEF and/or Distributed CEF is enabled on GSR and ESR platforms. It is possible that due to memory or some other software related issues, CEF may get disabled. In that scenario, cef can manually be enabled by entering the following command.

ip cef distributed *

* show ip cef and show cef line can be used to verify if CEF is operational.

Mention any scaling limitations w.r.t CEF or dCEF

Label Distribution Protocol (LDP)

LDP is responsible for distributing the labels for IP destination prefix in the MPLS network. Labels are assigned to every IGP learnt prefix that is in the global routing table. This global routing table is created and maintained by the IGP, which, in <CUSTOMER NAME> network, is selected to be OSPF. Essentially all IP destination prefixes will be either a loopback or circuit interface address. No customer IP addresses will be maintained in the global routing table.

The core P routers only have an understanding of labels that are associated with IP destinations in the OSPF internal routing table. They have no knowledge of labels related to routes in customer VPNs as these are created and distributed by the MP-BGP process between PEs only. Therefore, in the P network, a labelled IP packet is switched to the next-hop based only on the outer label (the one allocated by LDP from the global routing table) until it finally reaches its destination. In an MPLS-VPN network, this final destination will always be the egress- PE that originated the VPN route.

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Interface MTU size

As mentioned earlier, two levels of labels are needed to deliver MPLS-VPN services. The first level label is distributed by the LDP protocol, whilst the second level label is created by MP-BGP for VPN distribution as discussed in the next section.

When these two labels are placed into the frame they increase the frame size by 8 bytes (4 bytes per label). This can be problematic particularly on Ethernet interfaces which have a default Maximum Transmission Unit of 1500 bytes; bigger frame sized packets will be dropped if packets arrive with no fragment bit set. Note that with Ethernet encapsulation without dot1q encap, the actual layer 2 frame size is 1518 while with dot1q encap, the actual layer 2 frame size is 1522. With two label impostion, the actual layer 2 frame size becomes 1526 (or 1530 with dot1q encap) as shown in the Figure 28.

Figure 28 Layer 2 Frame with 2 MPLS Labels

However, it is possible to increase the MPLS mtu on an interface to accommodate the switching of packets bigger than 1500 size. The default MTU on Serial and POS interfaces is 4470bytes so frame increase of 8 bytes is not a big concern on these interfaces. The following command can be used on gigabit Ethernet interfaces in the <CUSTOMER NAME> network.

mpls mtu 1516

This will allow an MPLS frame with upto 4 labels (16 bytes) over the link. If any Ethernet switches are added into the core carrying MPLS frames they must also have their MTU increased.

Not

e

4 labels have been allowed to cater for future services on the network such as traffic engineering & FRR etc. In general, each additional service may require an increase in the label stack from 2 to something greater.

LDP Configuration and Design Recommendations

In this section list all the design and recommendations and configurations related to customer;s networks. Following are just example of them and may or may not apply to your customer

Mention any scaling limitations w.r.t LDP. Give details on any convergence results that you got from SPSE DIG or inhouse testing

To activating Label Switching on a router mpls ip command must be issued on each interface that connects P and PEs routers together. This should not be enabled on PE-CE connections.

By default Cisco router will enable TDP (Tag Distribution Protocol) when mpls ip is enabled on an interface. It is recommended to enable LDP globally by entering mpls label protocol LDP command globally using Cisco IOS CLI

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For proper operation of MPLS, LDP chooses an ip address as a router-id. It is important to note that the ip address chosen as router-id is routable, otherwise LDP will not be able to form the neighbor relationship with the adjacent nodes. On Cisco router, LDP router ID is, by default, determined as follows:

o The IP addresses of all operational interfaces are examined.

o If these IP addresses include loopback interface addresses, the largest such loopback address is selected as the LDP router ID.

o Otherwise, the largest IP address pertaining to an operational interface is selected as the LDP router ID.

However, the normal (default) method for determining the LDP router ID may result in a router ID that is not usable in certain situations. For example, an IP address selected as the LDP router ID might not be advertisable by the routing protocol to a neighboring router. Therefore, for <CUSTOMER NAME> network, it is recommended to manually set the router-id by entering the mpls ldp router-id <interface> command. The specified interface must be operational for its IP address to be used as the LDP router ID. In addition, force keyword should be entered to make sure the router-id takes effect immediately upon entering this command. However, care should be taken using this command since all the existing LDP sessions will be torn down if the router-id of the existing sessions is different from the newly selected ID.

It is recommended to enable logging of LDP neighbor state change using mpls ldp logging neighbor-changes.

As with OSPF, MD5 based authentication could be enabled on each link where LDP will be used to prevent any DoS attacks, and to help with configuration errors.

Not

e

The IOS CLI accepts “tag” and “mpls” command interchangeably for most cases. For example, “show tag tdp neighbor” and “show mpls ldp neighbor” produce identical output. In some cases, there is only an “mpls” command such as “mpls label protocol ldp”. It is recommended to use newer “mpls” form of the commands in the <CUSTOMER NAME> network.

Not

e

The “mpls ip” command merely enables LDP on an interface, and it does not control whether a packet is switched using the MPLS Label at all – this is determined by the Ethertype on an incoming frame & via various forwarding tables.

Following example shows the sample configuration for enabling MPLS in the <CUSTOMER NAME> network. Below is the sample configs . Please use your cusomter specific configs

hostname <insert hostname>

mpls label protocol ldp!mpls ldp logging neighbor-changesmpls ldp router-id Loopback0 force!interface Loopback0 ip address <address> <mask> no ip directed-broadcast!!inteface pos 0/0

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description <insert appropriate descriptor> ip address <address> <mask> ip ospf message-digest-key 1 md5 <Change Me> mpls ip mpls ldp neighbor <neighbor address> password <CHANGE ME>

!

inteface gig 2/0description <insert appropriate descriptor> ip address <address> <mask> ip ospf message-digest-key 1 md5 <Change Me> mpls ip mpls ldp neighbor <neighbor address> password <CHANGE ME> mpls mtu 1516

Network Services

MPLS/VPN ServicesThis section describes how the VPN services are offered by <Customer Name> using the MPLS-VPN concept.

MPLS-VPN

In MPLS VPN terminology the term PE (Provider Edge) refers to the provider edge router, where the CE (Customer Edge) connects to and the VPN are created. Each VPN is associated with one or more VPN routing / forwarding instances (VRFs). A VRF consists of an IP routing table, a derived Cisco Express Forwarding (CEF) table, a set of interfaces that use the forwarding table, and a set of rules and routing protocol parameters that control the information that is included into the routing table.

A one-to-one relationship does not necessarily exist between customer sites and VPNs. A given site can be a member of multiple VPNs. A customer site's VRF contains all the routes available to the site from the VPNs of which it is a member.

Packet forwarding information is stored in the IP routing table and the CEF table for each VRF. A separate set of routing and CEF tables is maintained for each VRF. These tables prevent information from being forwarded outside a VPN, and also prevent packets that are outside a VPN from being forwarded to a router within the VPN.

All MPLS VPN configurations are done at the PE router. The rest of the network merely switches labels and is not aware of the VPN structure or logical separation of customers. The core network is referred to as the P network in an MPLS VPN.

In order to enable MPLS VPN there are several implementation steps:

MP-iBGP Implementation

VPN Routing & Forwarding Table Definitions

PE to CE Routing Definition

The following sections discuss each of these areas in more detail and provide recommendations and design guidelines and configuration examples for <CUSTOMER NAME> network.

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MP-iBGP4 (Multi-protocol iBGP) Implementation

BGP is one of the vital components in enabling MPLS VPN Service. It is used to propagate VPN routing information. Various BGP attributes and extensions are used to distribute the VPN routes.

Distribution of VPN Routing Information

A service provider edge (PE) router can learn an IP prefix from a customer edge (CE) router via either static or dynamic routing protocols. In the most basic configuration, static routes can be configured on both the CE and PE router configuration. Alternatively, dynamic routing protocols, including BGP, RIP, EIGRP or OSPF can be used to share IP prefix information between provider and customer networks.

The IP prefix is a member of the IPv4 address family. After it learns the IP prefix, the PE converts it into a VPN-IPv4 prefix by combining it with an 8-byte route distinguisher (RD). The generated prefix is a member of the VPN-IPv4 address family. It serves to uniquely identify the customer address, even if the customer site is using globally non-unique (unregistered private) IP addresses.

The route distinguisher used to generate the VPN-IPv4 prefix is specified by a configuration command associated with the VRF on the PE router.

BGP distributes reachability information for VPN-IPv4 prefixes for each VPN. Since these are not IPv4 addresses, BGP provides Multi-Protocol extensions (see RFC 2283, Multiprotocol Extensions for BGP-4) which defines support for address families other than IPv4 and allows the distribution of these VPN-IPv4 routes. It propagates VPNv4 reachability information, among the PE (or RR) routers only. The reachability information for a given VPN is propagated only to other members of that VPN. The BGP multi-protocol extensions identify the valid recipients for VPN routing information. All the members of the VPN learn routes from other members enabling them to communicate with each other. The entire operation of distributing the VPN routes is illustrated in the Figure 29 MP-BGP VPN Route Distribution example.

Figure 29 MP-BGP VPN Route Distribution example

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BGP communication takes place at two levels: within IP domains, known as autonomous systems (interior BGP or IBGP) and between autonomous systems (external BGP or EBGP). PE-PE or PE-RR (route reflector) sessions are IBGP sessions, and PE-CE sessions are EBGP sessions.

In addition, a PE router binds a label to each customer prefix learned from a CE router and includes the label in the network reachability information for the prefix that it advertises to other PE routers. When a PE router forwards a packet received from a CE router across the provider network it labels the packet with the label learned from the destination PE router. When the destination PE router receives the labelled packet, it does a MPLS lookup for the corresponding vrf and it pops the label and uses it to direct the packet to the correct CE router

Use of VPNv4 Route Reflectors

In this section you should also mention the number of recommended IBGP and MPiBGP sessions that an RR can handle. Also scale number for number of routes. The scale numbers should be in conjunction with scale numbers provided for IGP/LDP

The ability for route reflectors to adequately cater for all PE’s in the network is a function of the number of VPNV4 routes the RR has to hold, the number of PE peerings and the frequency of churn (VPNv4 routes being advertised and withdrawn). When RRs are used to peer the PEs in a MPLS/BGP network, the RRs will hold all the VPNV4 routes advertised by all the PE’s. In other words every route belonging to each customer network must be held in the RR for distribution to all other PEs or RRs. Scalability problems could arise if the number of VPN routes were very large as RR’s could potentially exhaust memory resources.

Figure 30 VPN route distribution using partitioned RRs shows one of the possible solution to address this problem and make MPLS VPN deployment scalable is to use route reflectors, but partition them in such a way that each partition would carry routes for a subset of the VPN’s provided by the <Customer Name> network. Thus, no single Route Reflector is required to maintain all routes for all the VPNs.

The figure below is for a particular customer. In your LLD you should use naming convention used by your customer

Figure 30 VPN route distribution using partitioned RRs

The mechanism for partitioning RR’s is via the route-target using a BGP command called bgp rr-group. With this command, each RR will only hold routes that match the specified route-targets.

If RR’s are to be partitioned several design issues must be considered in the <CUSTOMER NAME> network;

Location of Route Reflectors – ideally it would be ideal to deploy reflectors in various physical locations so that a single failure would not impact operations.

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Partitioning of Route Reflectors – How do you decide on which route reflectors carry which partitions (route targets)? Ultimately in a very large network, there will be many route reflectors each carrying a subset of the VPN partitions as shown below.

Below is the sample configs . Please use your cusomter specific configs

Route Reflector Configuration-----------------------------

ip extcommunity-list 1 permit rt 23756:1001

router bgp 23756 address family vpnv4 bgp rr-group 1 neighbor <pe1> activate neighbor <pe1> route-reflector-client neighbor <pe1> send-community extended

PE Router Configuration-----------------------

ip vrf custA rd 23756:100 route-target both 23756:100 route-target export 23756:1001

Route Reflector redundancy – There would need to be at least two route reflectors holding the same information, in the event there is a failure of one, the other can still provide VPN route information as shown in Figure 31 Route Reflector Redundancy in the <Customer Name> Networks.


Figure 31 Route Reflector Redundancy in the <Customer Name> Networks

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There are a total of <Put the actual number of RRs here> RR in the <Customer Name> network. Each RR is a <Equipment name with the memory>. We recommend deploying RR partitioned into two groups (This may change with some customers) with two RR in each group in the <Customer Name> network. Each group of RR can be assigned to serve few regions or partitioned can be made based on the route-targets that each RR will serve in the <Customer Name> network. This way each group of RRs will serve only a certain number of VPN customers and carries only a subset of routes instead of carrying the routes for all the customers. The PE routers could then connect to the two RRs in the corresponding group for the VPN information they require which would cut down the overhead of each RR holding all routes distributing all VPN routes to all peers. Doing this would provide <CUSTOMER NAME> with a scalable solution as the network grows. Alternately, a full mesh can be created between route-reflector if partition is not desired at this time.

In addition, it is recommended to configure both route-reflectors within each group with different cluster ids which otherwise may create issues if the IBGP sessions between PE and RR fail.


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Figure 32 Redundant Route Reflectors with same cluster-id.

The paragraph below is for a particular customer. In your LLD you should use naming convention used by your customer

In the above example, if iBGP session between JRC edge router and RR2 and KMR edge router and RR1 fails, the VPNv4 routes received by RR1 will be forwarded to RR2 but updates will be rejected due to same cluster ID. It is very unlikely that such a double failure will occur in the network but as a best practice, it is commended to place both RR in different clusters. By default, RR Cluster ID is chosen as the BGP Router-ID. However, it is advisable to set Cluster-ID manually on RR using the cluster-id configuration command.

Below is the sample configs . Please use your cusomter specific configs

On Route-Reflectors

router bgp 23756bgp cluster-id <loopback 0 ip address>

Autonomous System Number

An autonomous system (AS) number is required for MP-BGP peerings. By convention this value is also used in Route Distinguishers to create IP-VPNv4 addresses and route-targets, although it is not necessary they be the same as the AS number. <CUSTOMER NAME> will be using <Customer’s AS number>

MP-iBGP Authentication

Cisco implementation of BGP allows for MD5 authentication between BGP peers. This authentication provides some protection against accidental or malicious BGP peering in the network. It is possible to configure a unique password for every peer. However this may be administratively difficult to manage, particularly for eBGP links. Hence, a single password for all internal peering only is recommended.

neighbor <xxxPE> password <shared password between peers>

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Use of BGP Peer-groups

BGP peer-groups provide a way to group individual BGP peers with common policies to enable efficient update calculation and simplifies configuration. This method of grouping neighbors together for BGP update message generation reduces the amount of system processing resources needed to process the routing table. This method, however, has the following limitations:

All neighbors that shared the same peer-group configuration also had to share the same outbound routing policies.

All neighbors had to belong to the same peer-group and address-family. Neighbors configured in different peer-groups cannot belong to different address-families.

These limitations existed to balance optimal update generation and replication against peer-group configuration. These limitations also caused the network operator to configure smaller peer-groups, which reduced the efficiency of update message generation.

The introduction of the BGP Dynamic Update Peer-Groups feature separates BGP update generation from peer-group configuration. The BGP Dynamic Update Peer-Groups feature introduces an algorithm that dynamically calculates BGP update-group membership based on outbound routing policies. This feature does not require any configuration by the network operator. Optimal BGP update message generation occurs automatically and independently. BGP neighbor configuration is no longer restricted by outbound routing policies, and update-groups can belong to different address families.

As dynamic peer-groups take care of the update generation, simplification of the configuration can be achieved using either standard peer-group configuration or peer-templates. We therefore recommend the dynamic peer-groups (for update generation efficiency) and standard peer-group configuration for the <CUSTOMER NAME> network for the MPLS VPN deployment.

You need to make sure you clearly articulate what is bein recommended for this specific customer

Use of Path MTU discovery

Every TCP session has a limit in terms of how much data it can transport in a single packet. This limit is defined as the Maximum Segment Size (MSS) and is 536 bytes by default on the PE-routers. This means TCP will take all of the data in a transmit queue and break it up into 536 byte chunks before passing packets down to the IP layer. Using a MSS of 536 bytes ensures that the packet will not be fragmented before it gets to its destination because most links have a MTU of at least 1500 bytes.

The problem is that using such a small MSS value creates a large amount of TCP/IP overhead, especially when TCP has a lot of data to transport like it does with BGP in the MPLS VPN environment. The solution is to dynamically determine how large the MSS value can be without creating packets that will need to be fragmented. This is accomplished by enabling "ip tcp path-mtu-discovery" (a.k.a. PMTU). PMTU allows TCP to determine the smallest MTU size among all links between the ends of a TCP session. TCP will then use this MTU value minus room for the IP and TCP headers, as the MSS for the session. If a TCP session only traverses Ethernet segments then the MSS will be 1460 bytes. If it only traverses POS segments then the MSS will be 4430 bytes. The increase in MSS from 536 to 1460 or 4430 bytes reduces TCP/IP overhead, which helps BGP converge faster.

Increasing Interface Input queue and SPD thresholds

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Large numbers of interface input queue drops are a very common problem for PE routers with large number of BGP peers. When MP-BGP is advertising thousands of VPN routes to many peers TCP will transmit thousands of packets in a short period of time. Other PE routers will receive these packets and send TCP acknowledgements to the advertising PE router. If the acks come in at a receiving rate faster than the route-processor can handle, it will cause the packets to be buffered in the interface input queue. This queue by default is only 75 packets deep. In addition, there is a SPD (Selective Packet Discard) algorithm, which plays an important role in selectively removing the non-routing packets from processor's input queue in the case of congestion so that only routing packets can be processed. However, SPD queue is by default is only 100 deep. Therefore, TCP acks can potentially fill the 175 spots of input buffering leading to large number of dropped packets.

Increasing the interface input queue depth (hold-queue <1-4096> in) will help reduce the number of dropped TCP acknowledgements which reduces the amount of work BGP has to do to converge. Similarly the SPD parameters can be tuned using the following commands

Configure router for more SPD headroom and SPD extended headroom

ip spd mode aggressive ip spd headroom <a> ip spd extended-headroom <b> ip spd queue min-threshold <c> ip spd queue max-threshold <d>

For a large MPLS VPN network, it is recommended to extend both the input queue and spd thresholds. As a intitial value, input hold queue can be increased to 1500-2000. However, the optimum values can be obtained by constantly monitoring and tuning the input queue drops until drops have stopped. . To check if there is any drop following command can be used:

Router#show int <name> | include input queue

MP-BGP Configuration

Once neighbors are listed under the BGP process, Cisco IOS by default considers the neighbors to exchang ipv4 NLRIs. However, for MPLS VPN, VPNv4 prefixes need to be exchanged and for that neighbors explicitly need to be activated under address-family. However, it is recommended to disable the default BGP behavior using no bgp default ipv4-unicast. The following shows a generic MP-BGP configuration that could be applied to each PE router in the <CUSTOMER NAME> network.

hostname <insert hostname>!interface Loopback0 ip address </32 address> no ip directed-broadcast!router bgp 23756 no synchronization no bgp default ipv4-unicastno auto-summarybgp router-id <loopback 0>

bgp log-neighbor-changes! xxxPE peer group (xxx – Site / Region name) neighbor <xxxPE> peer-group neighbor <xxxPE> remote-as 23756 neighbor <xxxPE> update-source Loopback0 neighbor <xxxPE> password <password>

! xxxPE peer groups definition (complete with PE’s loopback0 address) neighbor <neighbor 1 address> peer group <xxxPE> neighbor <neighbor 2 address> peer group <xxxPE> ! - - - List all PEs in the cluster / region “peer-group xxxPE” - - - - no auto-summary

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address-family vpnv4 neighbor xxxPE activate neighbor xxxPE send-community extendedexit address-family

Creating VRF DefinitionsIn this section give scaling numbers for number of vrfs that can be configured on a given PE

The VRF is the basis for providing VPN services in MPLS. There will be a VRF table defined on every interface that connects to one of the edge services in the <CUSTOMER NAME> network.

Each VRF definition includes the following components;

A case sensitive name which identifies the VRF

A Route Distinguisher to uniquely identify IPv4 routes coming in on this customer interface

Import and export route targets defining export and import attributes for routes

Optional route-maps to further define the granularity of route export/imports

VRF Name

The VRF name is simply a unique name used to identify the VRF and the routes it contains. It is suggested the name be short and lower case if possible for operational ease. In addition, a description can be added to the vrf using the description command in the vrf sub-mode.

ip vrf vpnadescription customerA vpn

Route-Distinguisher

Each VRF must have a unique RD (Route Distinguisher) which will have the following format:

<AS>:<Unique Number>

where,

<AS> is the 16-bit autonomous system number allocated to the network. This will be set to the value <Customer AS #>and will also be used for all MP-BGP configurations

<Unique Number> A unique 32 bit number within the AS that is allocated by <CUSTOMER NAME>

In the situation where multiple sites of the same customer are connecting to the same PE router, each interface will use the same VRF definition, as they would normally be part of the same routing policy. This would give the customer sites peer access to each other via the PE.

Route-distinguisher Allocation schemes and Recommendations

There are three different approaches to allocate route-distinguishers for a given VPN in the MPLS VPN network.

Approach #1 - Unique RD for each VPN

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A unique RD value can be assigned for each VPN. For example: If there are three sites belonging to customer A connected to three different PEs, a same Rd value e.g. <Customer AS #>:100 can be assigned at each location as shown in Figure 33. Though this looks like a simple and straight forward approach, unfortunately, this option prevents from offering load sharing to the VPN client in the presence of route-reflectors which is the case in the <CUSTOMER NAME> network. If load sharing is not a requirement, then this scheme may be useful (as it reduces the memory requirements at the PE routers).


Figure 33 Unique RD per each VPN

Approach#2 - Unique RD per PE for each VPN

An alternative to the first approach is to assign a unique RD per PE for each VPN. In other words, for a given VPN, a unique RD value will be assigned on each PE. This is illustrated in theFigure 34. Note that, with this approach, routes received from multiple interfaces belonging to the same VPN on a particular PE will share the same RD value. However, each PE will assign a unique RD. The main advantage of this approach is that it allows iBGP load balancing. However, the drawback of this scheme is that extra memory is required to hold the additional paths at the PE-routers. This is the recommended scheme in the case where Route Reflectors are deployed.


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Figure 34 Unique RD per site for each VPN

Approach# 3 - Unique RD per PE per interface for each VPN

Approaches 1 and 2 could be used in the simple or overlapping VPN requiring any-to-any connectivity. However, implementing topologies such as hub and spoke etc. is not easy using approach 1 or 2. For Central or hub and spoke topologies, a PE may have more than one interface belonging to the same VPN but the connectivity requirement on one interface is different from the other interfaces. Approach 3 offers a solution to this problem by assigning a unique RD for each VRF per interface. The main advantage of this approach is to uniquely identify the site that has originated a route and enables the implementation of complex topologies. However, this capability comes at a relatively higher cost in terms of memory consumption and the number of VRFs to be configured. Because of these issues, this method is not recommended for simple VPNs. Moreover, BGP communities and Site-of-Origin (SOO) may be used to identify where a particular route originated. This scheme is only recommended for Hub & Spoke scenarios where multiple spoke sites are connected to the same PE router.

For <CUSTOMER NAME> network, we recommend to use scheme <Put here the scheme number and why its being used>

VPN Route Target Communities

The distribution of VPN routing information is controlled through the use of VPN route target communities, implemented by border gateway protocol (BGP) extended communities. Distribution of VPN routing information works as follows:

When a VPN route learned from a CE router is injected into BGP, a list of VPN route target extended community attributes are associated with it. Typically the list of route target community values is set from an export list of route targets associated with the VRF from which the route was learned.

An import list of route target extended communities is associated with each VRF. The import list defines route target extended community attributes a route must have for the route to be imported into the VRF. For example, if the import list for a particular VRF includes route target communities A, B, and C, then any VPN route that carries any of those route target extended communities --- A, B, or C --- is imported into the VRF.

The import and export values for route-targets can match the RD value for the VRF although they don’t need to be the same. The RD uniquely identifies customer IPv4 routes and the route-targets define import export policies for routes into and out of the VRF. Using the same route-target and RD values simplifies the configuration and management of it.

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The default route-target for <CUSTOMER NAME> VRFs will be equal to the RD presented above. Additional route-targets may be required given the route import & export policies needed.

The Table below is for a particular customer. In your LLD you should use the right nomenclature

Table 7 RT/RD Allocation

VRF Name RD Default Import

RT

Default Export

RT

custA 23756:100 23756:100 23756:100

cust2 23756:101 23756:101 23756:101

Cust3l 23756:102 23756:102 23756:102

2-15

VPN Topologies

Full Mesh

An Intranet VPN is the simplest way of deploying a VPN using MPLS. It essentially consists of all sitesof the same customer to directly peering with each other. From the customer's perspective, all of its sitesappear one hop away from each other. In reality a customer's IP packet may transit more than one corenode, though the customer will not see this.Each of the sites exchanges VRF routes directly with its peer. Note that only routes that originate fromthat VRF are exchanged. The result is that the customer's VRF table in each PE holds an identical set ofroutes and each customer route is reachable via the next hop PE.

Hub and Spoke

One of the advantages of MPLS VPNs is the full peering that is available between customer sites.However this is not always the ideal situation for some customers who may require a hub and spoketopology where all traffic between spokes must pass through the hub. The hub will have the knowledgeof every destination, whilst the spoke will send traffic to the hub site for any destination. The hubtherefore is the central transit point between spoke sites. It can then control access between spoke sites.Hub and spoke topologies require a special configuration. The Hub site requires two connections(sub-interfaces) to the PE. One will be to import all spoke routes into the hub while the other will beused export hub routes back to the spokes.This simple example concentrates on using dynamic routing for the distribution of all routinginformation. Static routing could also be used just as effectively, by placing a default route at spoke,which would then be imported to all the spoke VRF's. Each spoke VRF would then only need a singleroute to get to the hub.

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Exranets

Customers with Unique Addresses

The creation of an Extranet is simply a matter of importing/exporting routes between the VRF's of twoor more customers. If IP address overlap between customers is not an issue, that is, the IP address spaceis unique between customers, then routes could be imported directly between the VPN_<CUSTOMER>VRF tables.

Customers with Overlapping Addresses

If customers wishing to participate in an Extranet share the same address space, or there is the possibilityat some stage at new Extranet members will cause addressing problems, then address translation tounique addresses (provided by the service provider) must occur before traffic is allowed into theExtranet.

Extranet NAT at a Common Service Point

NAT can be done at a central point managed by Service Provider. Each customer will have a physicallyseparate NAT gateway which is connected to a VRF in their respective Intranet VPN's. The VRFconnected to the NAT gateway will have the route of the translated addresses from the other customerinjected into it. So a route is injected into the VRF of Customer 2 Site B and a separated route is injectedinto the VRF of Customer 1 Site A. This way each of the customers can participate in an Intranet, viathe two NAT gateways. The NAT gateways could also be firewalls, with a NAT function. Thereforeadditional security could be provided between the Extranet customers.

Extranet NAT at Customer Edge

NAT can also be done at the customer edge. The example used here is that the CE can only connect tothe PE using a single 10BaseT/FL interface. So Extranet/NAT and Intranet/non-NAT traffic must travelover the same interface to conserve hardware resources at the PE. In most situations the PE/CEconnection would be over a physical interface of some sort which could support sub-interfaces (NAT andnon-NAT)If the CEs were owned by the customer, then they would be responsible for creating the translations onthe interfaces going to the Extranet VRF, and agreeing on the addresses to be used. Service Providerwould be responsible for creating the VRF's and injecting the translated routes, if static routing wasbeing used. A more desirable situation would be if Service Provider provided a managed router service.This would mean Service Provider would have control all the way to the CE, and could provide andend-to-end managed NAT service between the CEs. Both customers VRF tables will have the translatedroutes injected into them so that packets can be routed in the Extranet. A special route-map and virtualinterface on each of the CE NAT routers, prevent any translation occurring for traffic destined to theirown Intranets. Intranet traffic would be classified as any packet with a destination address in thecustomer intranet space.Since translations are being done at both sites into the Extranet, static NAT translations would berequired for each host address that required Extranet communication. If dynamic translation was done,there would be no way of knowing what NAT address was allocated to each inside host.

Controlling route exports in extranets

Route-maps are very useful if you want to avoid populating the Customer VRF's with unnecessaryExtranet routes. This assists in conserving memory and provides a basic form of security (no route noaccess). Each customer VRF will have its standard route-targets to import/export routes for their

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Intranets. These are the first two route-target commands shown in the configuration for each VRF.Next, each VRF has an export map defined. This export map will set a specific route-target value(referred to as an extended community attribute in BGP) for the Extranet route defined. By usingroute-targets, we can selectively import the only the routes the CE needs to participate in an Extranet.Individual host addresses could also be explicitly specified and exported using route-maps.

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PE-CE Routing Implementation

In this section you need to also highlight scale numbers for different routiing protocols between PE-CE. For example the max number of seesions for OSPF. Or max number of routes that would be accepted per session etc. If dampening is used then parameters for it.

A VPN Routing and Forwarding table (VRF) is associated with each CE interface on the PE and contains the routing information associated with that site. A PE-CE routing protocol is necessary so that the PE table can be populated with the customer’s routes.

The following routing protocols are available to operate between the PE and CE in a MPLS VPN environment;

Static

RIPv2

eBGP

OSPF

EIGRP

BGP, RIP, and EIGRP protocols have been modified to understand VRF tables by the use of a feature called address families. Address families define the VRF contexts that the routing protocol will operate in.

Note that the routing protocol that operates between the PE-CE is independent of any IGP that may run inside the VPN customers network. Routes learnt at the local VPN site by the customer IGP will be redistributed into the PE-CE routing protocol to populate the VRF. It is important to understand that no special MPLS configurations are needed at the Customer Edge. Only standard IOS routing commands are required.

<CUSTOMER NAME> is planning to use <Put the name of routing protocols that the customer would use> for the PE-CE routing protocols

Connectivity via Static RoutingIt is recommended to use static routing if the customer is small or is a stub site and the IP addressing of devices is unlikely to change. The CE router would have a default route pointing in the direction of the MPLS cloud, whilst the PE would require a similar static route inserted into the appropriate VRF table associated with the customer interface. In order to tell the remote VPN sites (or PE routers) about the local VPN routes, these customer specific vrf static routes on the each PE router need to be redistributed in the customer specific BGP address-family.

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The static route in the PE would have the following format indicating name of the VRF table and also the outgoing interface and its IP address.

Static routing configuration - PE

ip route vrf CustomerA 10.0.0.0 255.0.0.0 serial1/0 <CE link adress> [permanent]

router bgp 23756address-family ipv4 vrf customerAredistribute static

The CE route would consist of the default route pointing to the next hop ip address/interface of the PE.

Static routing configuration – CEip route 0.0.0.0 0.0.0.0 <PE link adress>

Routing Stability

With static routing, if the PE-CE link fails, the static route associated with the interface will be removed from the routing table. In the case of the PE, this will cause an MP-iBGP routing update to be forwarded to all other PE peers. To prevent such a behavior, the keyword “permanent” can be appended when configuring the static route. This will cause the static route to remain in the routing table regardless of the interface status. This obviously reduces the BGP update messages and improves VPN route convergence, however, such an improvement comes at the cost of unnecessary backbone bandwidth utilization. This is because the packet will get forwarded through the core all the way to the remote PE and only then will get dropped if the directly connected link is down.

RIPv2 configuration (PE to CE)RIPv2 could be used as a PE-CE routing protocol and is included here as an example. RIPv2 is a distance vector protocol and will periodically send the whole routing table to each neighbor to maintain synchronisation of routes. For managed CE routers, dual homing and more sophisticated routing policy eBGP should be used as the PE-CE protocol.

PE Configuration

The following example shows the configuration of the PE side of the RIPv2 circuit. In the example, the CE device is connected to a PE via a serial link.

router rip version 2 ! address-family ipv4 vrf CustomerA version 2 redistribute bgp 23756 metric 5 network <pe-ce network> no auto-summary exit-address-family!!interface serial3/0 Description Circuit to Customer1 ip vrf forwarding CustomerA ip address a.b.c.1

router bgp 23756

address-family ipv4 vrf customerA

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redistibute rip

…

The address-family under RIP process indicates RIPv2 that this routing instance is associated with a VRF for CustomerA. Any interface on this PE that has this VRF defined will participate in RIPv2 routing if they are part of <pe-ce> network.

The redistribute bgp command allows routes BGP has learnt from other VRF’s that have been brought into the VRF CustomerA (subject to the policies, route-targets etc…) to be redistributed to the RIPv2 routing instance for forwarding to the CE. Similarly, these local site routes need to be redistributed into MP-BGP so that these are advertised to the remote PE and ultimately to the remote VPN sites.

CE Configuration

The CE uses a standard RIPv2 configuration. No special VRF configurations are necessary

RIPv2 CE Configuration router rip version 2 network <ce-pe network> redistribute <customer IGP>

interface serial0 Description Connection to PE router ip address a.b.c.2…

eBGP configuration (PE to CE)eBGP routing would be the most appropriate protocol to use if the CE was dual homed to multiple PE’s or extensive policy routing features are needed. By using eBGP between the PE and CE routing loops can be avoided using various mechanism within BGP. No routing information is lost as BGP (either eBGP or MP-iBGP) is used along all the paths, i.e. between PE-CE and PE-PE. <CUSTOMER NAME> is planning to use EBGP to inject routes from larger customers. eBGP also has the ability to automatically prevent routing loops.

The BGP configuration of the PE depends on whether the customer has many sites using eBGP as the PE-CE protocol and whether those CE sites are using unique AS numbers or are all using the same AS number.

Configuration at the PE

Unique AS per customer site

The example in this section shows the BGP configuration for connecting CE’s from one customer, each of which uses a unique AS.

shows a number of CE networks each with a different AS number. Therefore if the network at CE A wished to talk to the network at CE B it would have to pass via the MPLS-VPN core and the AS_PATH followed would be 23756 65001. The AS number 23756 will appear in the AS_PATH as the CE packet transits the <CUSTOMER NAME> core.

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In this scenario if one (or more) of the CE’s were dual homed, routing loops would be avoided due to the standard AS path check done on incoming routes to the CE from the PE.

The figure below and the above last two paragraphs are for a particular customer. In your LLD you should use naming convention used by your customer

Figure 35 PE-CE eBGP with unique AS

The eBGP configuration for the PE-CE link is shown in the following diagram.

The configs below is for a particular customer. In your LLD you should use customer specific configs

router bgp 23756 …. address-family ipv4 vrf CustomerA neighbor <customer link address> remote-as 65001 neighbor <customer link address> activate no auto-summary no synchronization exit-address-family ! ….interface serial3/0 Description Circuit to CE A ip vrf forwarding CustomerA ip <customer link address>

Note that the above configlet is showing only the IPV4 address family section of the BGP configuration related to the VRF.

For every CE that requires a BGP peering there must be a corresponding address family with appropriate neighbor commands. The configuration at the CE is standard BGP (as if it were connecting to another CE).

Single AS for all customer sites

There may be occasion where customers wish to use the same AS number at all their sites. This would be typical in an existing BGP customer network where the customer is migrating to an MPLS-VPN network and does not want to have to change their BGP configurations.

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Figure 36 PE-CE eBGP with single network wide AS

As shown in the Figure 36, CE B rejects the routes coming from CE A when it sees its own AS number in the BGP AS Path. This is standard BGP loop prevention mechanism. As a result, CE B will not be able to communicate with CE A.

AS-Override

To solve this problem, the PE can be instructed to override the customer’s AS number before forwarding the BGP update to the customer. This can be achieved by using BGP neighbor parameter “as-override” configuration command. This is illustrated in the following configuration example:

The configs e below is for a particular customer. In your LLD you should use customerspecific configs

router bgp 23756rddress-family ipv4 vrf customerAreighbor <customer A address> as-override

This configuration is needed at the PE which then replaces the customers AS number (in this case AS 65001) with the providers AS number (AS 23756) so that the receiving CE will accept the routes as it will not see its own AS in the path. With ASN override configured, the PE does the following:

If the last ASN in the AS_PATH is equal to the neighboring one, it is replaced by the

provider ASN

If last ASN has multiple occurrences (due to AS_PATH prepend) all the occurrences are

replaced with provider-ASN value

After this operation, normal eBGP operation will occur and the provider AS will be added

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to the AS_PATH

Site-of-Origin

By enabling as-override feature, loop detection using the AS_PATH is disabled. This obviously will cause problems if the CE is dual-homed, as is the case for CE B in Figure 36. A BGP extended community attribute, referred to as the Site-of-Origin (SOO) addresses this issue.

The SOO prevents routing loops when a site is multi-homed and the as-override feature is being also being used. This is achieved by identifying each customer site with a unique SOO. The SOO, similar to route-target is a BGP extended community and is denoted in the same format as route-target.

All routes originating from a customer site are identified with a SOO by the eBGP process on ingress to the PE. If those routes for some reason end up back at the originating PE, they will not be re-advertised to the CE as the SOO will match that of the site.

Note that a site may consist of many routers each containing the same routing information. If several of these routers are connected to the MPLS-VPN backbone as CE’s, they will still use the same SOO. Only when the sites are different will a different SOO be used.


router bgp 23756 …. address-family ipv4 vrf CustomerA neighbor <CE neighbor address> remote-as 65001 neighbor <CE neighbor address> activate neighbor <CE neighbor address> as-override neighbor <CE neighbor address> routemap setsoo in no auto-summary no synchronization exit-address-family ! ….interface serial9/0 Description Circuit to CE A ip vrf forwarding CustomerA ip <PE-CE link address>

route-map setsoo permit 10 set extcommunity soo 23756:1002

Above example shows the PE configuration when using as-override and SOO. The neighbor <CE neighbor address> as-override command causes AS 65001 in the AS_PATH to be replaced with AS 23756. The neighbor <CE neighbor address> routemap setsoo in command causes all incoming routes from the CE (CE A in this case) to have SOO 23756:1002 set in the extended community attribute.

Note

What is not obvious is that the same command neighbor <CE neighbor address> routemap setsoo in also causes the PE to check routes it is distributing to the CE for the same SOO. If there is an SOO match then the routes are not re-advertised to the CE.

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Routing Stability

The eBGP route dampening feature can control flapping routes from the CE. The “maximum route limit” command described in the following section and the BGP “neighbor x.x.x.x prefix-limit” command will allow the limiting of the number of routes installed in the VRF and redistributed in MP-iBGP.

Controlling number of VRF routes

It is possible that an excessive number of routes get distributed into the VRF due to some problem in the customer network. In the MPLs VPN network, multiple customers connect to the same provider edge router. Therefore it is very important to protect the resources such as memory, and CPU on the PE routers.

If the PE-CE protocol is BGP, the numbers of routes received from the CE can be controlled at each site by using the maximum-prefix command as shown below.


router bgp 23756address-family ipv4 vrf customerAneighbor <ce neighbor address> {maximum-prefix maximum [threshold]} [restart restart-interval] [warning-only]

Table 8 BGP Timer Definitions

maximum Maximum number of prefixes allowed from the specified neighbor. The number of prefixes that can be configured is limited only by the available system resources on a router.

threshold (Optional) Integer specifying at what percentage of the maximum-prefix limit the router starts to generate a warning message. The range is from 1 to 100; the default is 75.

restart (Optional) Configures the router that is running BGP to automatically reestablish a peering session that has been disabled because the maximum-prefix limit has been exceeded. The restart timer is configured with the restart-interval argument.

With the maximum prefix command, when the threshold is reached, the BGP session is terminated. Alternately, maximum-prefix command can be augmented with warning-only key word. This allows the router to generate a log message but keeps the bgp session up instead of terminating it when the threshold is reached. If warning-only key word is not configured, BGP session is torn down as a result of reaching the threshold and will stay down indefinitely. Manual intervention is required to bring the session up unless restart-interval is configured to bring the session up automatically after the restart-interval has elapsed.

There is no default limit on the number of prefixes that can be configured with this command. Limitations on the number of prefixes that can be configured are determined by the amount of available system resources and are configured by the network operator. Peering sessions will be disabled (by default) when the configured maximum number of prefixes has been exceeded.

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The BGP maximum route knob allows to control the routes if the PE-CE protocol is BGP. However, there is no such per neighbour capability available in the other dynamic protocols to control the routes received from the CE sites. However, alternately, the total number of routes in a customer VRF can be controlled by using the “maximum routes” command inside the VRF configuration as follows.The configs below is for a particular customer. In your LLD you should use customer specific configs

ip vrf CustomerA rd 23756:1000 route-target both 23756:1000 maximum routes 1000 warn-only | warn-threshold

In the above example, the number of routes allowed in the VRF is limited to 1000. The “warn” keyword does the following:

warn-threshold Rejects routes when the threshold limit is reached. The threshold limit is a percentage of the limit specified, from 1 to 100.

warn-only Issues a SYSLOG error message when the maximum number of routes allowed for a VRF exceeds the threshold. However, additional routes are still allowed.

For <CUSTOMER NAME> network, we recommend that the both the BGP per neighbor and VRF maximum routes command should be included with every PE-CE BGP session and VRF definition.

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Additional MPLS VPN Services

Internet Access for MPLS/VPN customers

There are two basic design models for combining Internet Access with MPLS / VPN services.

Internet access is offered through global routing on the PE routers. There are 2 implementation options.

o A first one is to implement packet leaking shortcut between a VRF and the global routing table. This option has a number drawbacks and must be avoided.

o A second implementation option is to use separate physical or logical interfaces for VPN and for Internet access. The physical or logical interface meant for Internet access will be placed in the global routing table. Ideally, the Internet interface (also called IPv4 link) will be implemented on a separate CE router, which permits to put the FW in customer site.

Internet access is offered through yet another VPN. This is called the Internet VPN (and associated Internet VRF). This solution has the advantage that the provider’s backbone is isolated from the Internet, resulting in improved security. A drawback is that full Internet routing cannot be implemented because of scalability problems and is therefore not recommended solution for ST.

Separate CEs for Internet Access and VPN Access

From the point of view of the VPN customer, the “separate CE” design model maps ideally on the situation where the VPN customer wants centralised and firewalled access to the Internet The customer managed firewall can provide NAT services in between the private VPN addressing and the public Internet addressing. The central customer site firewall gives the customer the ability to control security and Internet service policies. A drawback is that all the Internet traffic must flow through a central site.

For example, a large bank with hundreds of branches would not want to implement Internet access directly from each of the branches, as this would imply management of strict security policies at every site

The fig below is for a particular customer. In your LLD you should use customer specific figs

Figure 37 Internet Access from a VPN using separate CEs

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(difficult and expensive). The centralised FW approach with two CE routers is more appropriate solution.

It is worth to mention that default static routes will be injected into VPN and used by regional sites, but the default route can not be used for VPN traffic on central site. On the drawing above, the CE2 will be configured with a default route pointing to PE3 via IPv4 interface. For this reason, the CE1 (and CE2) have to have all the VPN routes in the routing table.

Central site shall learn the VPN routes dynamically with BGP4 or RIPv2 between CE1 and PE3. This is recommended approach as it allows greater flexibility and redundancy. For example, customer may want to implement two VPN CEs in central site to improve service availability.

In case of small number of regional prefixes, or if all regional prefixes can be summarized in a single aggregate route, static route can be implemented from CE1 to PE3 for VPN traffic.

Low-cost Internet Access (1CE + one/two access links)

The low-cost solution described in this chapter is not as secure as the one with two CE routers and firewall in customer site. The low-cost solution can therefore become very expensive if the security is compromised and intruder gains the access into customer’s VPN. Customers with sensitive data shall subscribe to secure Internet access from their VPN.

Therefore, the single-CE design for Internet&VPN access shall not be recommended to ST customers!

Two options exist to provide Internet connectivity from a single CE router:

Single access-layer connection for Internet and VPN traffic, and packet leaking on the PE.

Two logical PVCs or two physical connections between the CE and PE; one for VPN traffic (VPNv4 link) and one for Internet traffic (IPv4 link).

Single link option

The option with single link for VPN and Internet traffic represents serious risk for that VPN because of the “shortcut” that has to be created between the global routing table on the PE (i.e. the Internet) and the VRF.

PE2

MPLS Network

CE1

FW

InternetInternet

PE1

PE3

CE1

Central Site

Region. Site

Default route injected intoVPN

Data forwarding path fromregional sites to I nternet

CE2

VRF_RED interface (VPNv4)

Global routing tableinterface (I Pv4)

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No security mechanisms (e.g. packet filtering) are available on this shortcut. CE_Blue on Figure 38 below depicts this situation.

Packet leaking between a VRF and the global routing table is implemented with two IOS mechanisms:

A static route with a global next-hop can be configured in a VRF. Packets following this static route will end in the global address space at the next-hop router. Traffic originated at a customer site can thus be forwarded into the Internet.

Global static route can be defined pointing to a connected interface, which belongs to a VRF. This static route is further redistributed into IGP or BGP. Packets originated in the global address space will follow this route (in the global routing table) and will eventually be forwarded toward a CE router. Traffic originating in the Internet can thus be forwarded to the CE router.

Since the default route in the VPN points to the Internet, no additional default routing can be used in the customer VPN. In addition, when a customer site looses connectivity to the MPLS / VPN backbone, packets from other sites destined for the failed VPN site will be leaked to the Internet. This is another major security issue. In general, this option is also fairly complex to implement.

VPNv4 and IPv4 links

The two links between CE and PE can be implemented as two separate physical circuits (e.g. two E1 circuits) or as a two logical connections - for example the ATM PVCs. IPv4 link will terminate in the Global Routing table on the PE router, VPNv4 link will be assigned to the customer’s VPN.

Static default route will be configured on the CE for Internet access and it will point towards PE via IPv4 link. VPN routes will be in most cases uploaded to the CE with dynamic routing protocol (eBGP, RIPv2), but can be statically configured on the CE if number of prefixes is small.

The single-CE solution implemented with separated links for VPN and Internet traffic allows configuring packet filtering on IPv4 link on the CE router, but does not offer logical separation of two security zones (MPLS/VPN and Internet) with a firewall. It is mandatory to define a strict packet filtering rules in both directions: to and from the Internet. Outbound filter must for example prevent VPN packets to be leaked in the Internet (via default route) when VPNv4 connection fails. Inbound filter must clearly define the list of hosts and applications that can be reached from the global Internet. It is up to customer and service provider (ST) to define and implement desired security policy (i.e. packet filters) on a managed CE router.

If the customer uses private IP addresses, NAT would have to be implemented on the IPv4 link. Please note that static “one-to-one” translation is needed only for Internet servers, whereas the clients can be dynamically translated in a pool of IP addresses in a PAT-like mode.

Figure 38 Internet Access from a VPN – Single CE (two links in CEred, single link on CEblue)

In the end explain which option is being used

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Shared vrf-aware services

Network Address Translation for MPLS/VPN customers

The following configuration template can be used on customer’s CE router in case of private IP addressing in customer site. The example below shows two types of NAT translations:

Static on-to-one translation for servers in customer site, that must be reachable from the Internet

Dynamic NAT in overload mode (PAT) for PC clients.

Please note that NAT is only required on IPv4 link.

The config below is for a particular customer. In your LLD you should use customer specific configs

hostname CE!interface Ethernet0 description Customer site x ip address 10.10.10.254 255.255.255.0 !--- This is the inside local IP address and it's a private IP address. ip nat inside!interface Serial0 description CE-PE Internet link ip address 213.x.x.x 255.255.255.252 !--- This is the inside global IP address. !--- This is public IP address and it is provided by ST.

PE

MP-BGP

CE RED

vrf_ red global_ rt

VPNv4 link I Pv4 link

vrf_blue

CE BLUE

VPNv4 &I Pv4 link

!ip route vrf BLUE 0.0.0.0 0.0.0.0 <PE_loopb> global!

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ip nat outside!interface Serial1 description CE-PE VPN link ip address 213.x.x.x 255.255.255.252 !--- NAT is not performed on the VPNv4 link!!--- This statement makes the router perform PAT to overload the Serial0!--- IP address for all the End Stations behind the Ethernet interface !--- that are using private IP addresses defined in access list #1.ip nat inside source list 1 interface Serial0 overload!!--- This statement performs the static address translation for the Web server. !--- With this statement, users trying to reach 171.68.1.1 port 80 (www) will be !--- automatically redirected to 10.10.10.5 port 80 (www), which in this case !--- is the Web server.ip nat inside source static tcp 10.10.10.5 80 171.68.1.1 80!!--- This access list defines the private network !--- that will be network address translated using PAT overload mode. access-list 1 deny host 10.10.10.5access-list 1 permit 10.10.10.0 0.0.0.255!ip route 0.0.0.0 0.0.0.0 Serial0!

The fig below is for a particular customer. In your LLD you should use customer specific figs

Figure 39 NAT in CE router

Connecting Downstream ISPs to PE routers

Internet customers that require full Internet routing table (eg. a downstream ISP or multi-homed customer) to implement primary/backup or any other inter-domain routing policy will be in most occasions attached to the two iGW routers. If there’s a need to interconnect such customer in regional PoP, ST will install a PE router with sufficient memory and CPU power to hold the full Internet routes. Otherwise, the customer would have to install two eBGP sessions: one with iGW to download full Internet routes and another with the PE router to advertise its customers’ routes. This is required because next-hop-self feature is systematically applied on PE-RR and iGW-RR BGP neighborships.

PE CE

Webserv.

PC

VPNv4 link

I Pv4 link S0

S1 E0

10.10.10.5/24

10.10.10.x/24

.254

Static NAT translation10.10.10.5 <-> 171.68.1.1

Dynamic NAT inoverload mode

VRFip route 10.10.10.0/24 ->

S1@CE1

Global RTip route 171.68.1.1/32 ->

S0@CE1

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Remote Access (ASWAN/Security, Dial, DSL, Cable)

Wireless

VOIP

Inter-AS/CsC

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Traffic Engineering and Fast Reroute Technology Overview

Traffic Engineering Basics

Traffic Engineering is a powerful MPLS-based tool, which can be used not only to reduce cost for service providers (SPs) but to generate new revenues as well. One of the key functions of Traffic Engineering is to maximize the utilization of network resources. By making the SP’s network more efficient, Traffic Engineering reduces the cost of the network. Another function of Traffic Engineering is restoration. While delivering the same level of protection as SONET APS, Traffic Engineering restoration is more flexible and less costly. With Traffic Engineering, the SP may choose to protect only the set of links that are most vital to the entire network, and only the traffic which requires low loss probability. Traffic Engineering restoration increases the reliability of the SP’s network and improves the quality of the SP’s service. Alternatively, the SP may sell Traffic Engineering restoration as a premium service. Traffic Engineering helps the SP generate new revenue because it enables the SP to offer new services.

First, we introduce the concept of traffic trunks. Traffic trunks are aggregated micro-flows23 that share a common path. In the context of this document, a "common path" does not refer to the end-to-end path of the flows, but a portion of the end-to-end path within the service provider's network. Typically, the common path originates from the ingress of the service provider's wide area network to the egress of the service provider's wide area network. For example, all traffic originating from an IP address in San Jose and destined for an address in New York City may constitute a traffic trunk, and all traffic between an address in Palo Alto and an address in Washington D.C. another.

Optionally, we may require that all packets within a traffic trunk have the same class of service. For example, all ftp and telnet (priority 1) traffic between San Francisco and New York City may be considered a trunk, and all VoIP (priority 5) traffic between San Francisco and New York City another one.

23 A micro-flow refers to the packets travelling from a source to a destination using the same transport protocol and the same port number. For example, an ftp session between two IP hosts constitutes two micro-flows, one from the client to the server, and the other from the server to the client.

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Traffic Engineering creates one or more explicit paths with bandwidth assurances for each traffic trunk. It takes into consideration the policy constraints associated with the traffic trunks, and the physical network resources, as well as the topology of the network. This way, packets are no longer routed just based on destination, but also based on resource availability, and policy. The following section describes the operation of Traffic Engineering.

Figure 1 illustrates the operation of Traffic Engineering. Each step shown in the diagram is explained below.

Figure 40 - Traffic Engineering Mechanisms

The network operator must create a traffic model. Based on statistics collected from the routers, as well as administrative policies, the network operator needs to identify the traffic trunks within the network, and decide how these traffic trunks should be routed. The operator can use an off-line tool to optimize the traffic model. This does not mean that the operator is required to use the off-line tool to determine the routes for all traffic trunks. Typically, the operator identifies a full mesh of traffic trunks but administratively routes only the "top" N traffic trunks. On-line procedures are used for the rest of the trunks, as well as to handle failure situations. Traffic trunks could also be forwarded along routes computed by conventional IGP.

The router uses RSVP to set up Label Switching Paths (LSPs) and to reserve bandwidth at each hop along the LSPs. During the LSP setup process, any router within the network must perform admission control and/or preemption to ensure that resources are available to honor the reservation. After the paths are set up, the head-end routers forward the packets belonging to traffic trunks by placing them into the appropriate LSPs.

The following section breaks down Traffic Engineering into components and describes each component.

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Traffic Trunk Attributes

Traffic trunk attributes allow the network operator to describe the characteristics of traffic trunks. They must be granular enough to account for the different types of packets traversing the network, and detailed enough to specify the desired behaviour in failure situations. There are six traffic trunk attributes and each is described below.

Bandwidth

This attribute specifies the amount of bandwidth the traffic trunk requires.

Path Selection Policy

This attribute gives the network operator the option to specify the order in which the head-end routers should select explicit paths for traffic trunks. Explicit paths may be either administratively specified or dynamically computed.

Resource Class Affinity

This attribute is used to allow the network operator to apply path selection policies by administratively including or excluding network links. As will be shown later, each link on the network may be assigned a resource class as one of the resource attributes. Resource class affinity specifies whether to include or exclude links with resource classes in the path selection process. It takes the form of the tuple <resource class mask, resource affinity>. The "resource class mask" attribute indicates which bits in the resource class need to be inspected, and the "resource affinity" attribute indicates whether to explicitly include or explicitly exclude the links.

Adaptability

This attribute indicates whether the traffic trunk should be re-optimized. The re-optimization procedure is discussed in a later section.

Resilience

This attribute specifies the desired behavior under fault conditions, i.e., the path carrying the traffic trunk no longer exists due to either network failures or preemption. Traffic Engineering's restoration operation is discussed in a later section.

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Priority

Priority is the mechanism by which the operator controls access to resources when the resources are under contention. It is a required function to place all traffic trunks. Another important application of the priority mechanism is supporting multiple classes of services. We assign two types of priorities to each traffic trunk: holding priority, and setup priority. Holding priority determines whether the traffic trunk has the right to hold a resource reservation when other traffic trunks attempt to take away its existing reservation. Setup priority determines whether the traffic trunk as the right to take over the resources already reserved by other traffic trunks.

Resource Attributes

Resource attributes are used to describe the network links used for path calculations. There are three resource attributes, each of which is described below.

Available Bandwidth

This attribute describes the amount of bandwidth available at each setup priority. Note that the available bandwidth for the higher setup priority is always larger than that for the lower setup priority. This attribute needs not necessarily reflect the actual available bandwidth. In some cases, the network operator may oversubscribe a link by assigning a value that is larger than the actual bandwidth, e.g., 49.5 Mbps for a DS-3 link.

Resource Class

This attribute indicates the resource class of a link. Recall that the trunk attribute, resource class affinity, is used to allow the operator to administratively include or exclude links in path calculations. This capability is achieved by matching the resource class attribute of links with resource class affinity of traffic trunks. The resource class is a 32-bit value. The resource class affinity contains a 32-bit resource affinity attribute and an associated 32-bit resource class mask. .

Path Selection

Path selection for a traffic trunk takes place at the head-end routers of traffic trunks. Using extended IS-IS/OSPF, the edge routers have knowledge of both network topology and link resources. For each traffic trunk, the router starts from the destination of the trunk and attempts to find the shortest path toward the source (i.e., using the shortest path first (SPF) algorithm). The SPF calculation does not consider the links which are explicitly excluded by the resource class affinities of the trunk, as well as the links which have

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insufficient bandwidth. The output of the path selection process is an explicit route consisting of a sequence of label switching routers. This path is used as the input to the path setup procedure.

Path Setup

Path setup is initiated by the head-end routers. RSVP24 is the protocol which establishes the forwarding state along the path computed in the path selection process. The head-end router sends a PATH message for each traffic trunk it originates. The PATH message carries the explicit route computed for this traffic trunk. As a result the PATH message always follows this explicit route. Each intermediate router along the path performs trunk admission control after receiving the PATH message. Once the router at the end of the path receives the PATH message, it sends a RESV message in the reverse direction towards the head-end of the traffic trunk. As the RESV message flows toward the sender, each intermediate node reserves bandwidth and allocates labels for the trunk. Thus when the RESV message reaches the sender, the LSP is already established.

The following diagram is an example of the path setup procedure.

Figure 41 - Traffic Engineering Path Setup

Once you’ve decided to set up an LSP for a tunnel, you do that using RSVP with certain extensions to support this feature. In RSVP, the forward leg of the signaling message is called the path message, and the reverse leg is called the reservation message. So one of the extensions is that the path message can carry the source route in the new object. Resources are actually allocated on the reverse leg with the reservation message. In addition to bandwidth, which is an existing RSVP resource, there are extensions so that labels can be allocated and transmitted in the reverse direction on the reservation message.

24Note that the usage of RSVP in Traffic Engineering deviates from the original design goal of RSVP. Extensions to RSVP and the justification for using RSVP are discussed in a later section.

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In Figure 2 we’re establishing a tunnel from R1 to R9 along the path shown in the slide here. That path is included in the path message that is generated by R1, and it directs the path along the yellow arrows from the head of the tunnel to the tail.

In the reverse direction, the reservation message flows back on whatever series of hops was established by the path. At each hop the tag from the hop closer to the tail is received and programmed into the MPLS forwarding table. A new tag is allocated, and that new tag or label is sent upstream towards the head until eventually we get back to the head and the head knows that to send traffic down the tunnel, it should use label 49.

One feature of interest about the resulting LSP and about the MPLS tunnels under IOS in general is that they’re unidirectional. Traffic flows from the head to the tail, but there’s no automatic reverse direction. So you couldn’t for instance run an adjacency over one of these MPLS tunnels because the traffic’s one way.

Link Protection (FRR) Basics

Regular MPLS traffic engineering automatically establishes and maintains label-switched paths (LSPs) across the backbone using Resource Reservation Protocol (RSVP). The path used by a given LSP at any point in time is based upon the LSP resource requirements and available network resources such as bandwidth.

Available resources are flooded via extensions to a link-state based Interior Gateway Protocol (IGP), such as IS-IS or OSPF.

Paths for LSPs are calculated at the LSP headend. Under failure conditions, the headend determines a new route for the LSP. Recovery at the headend provides for the optimal use of resources. However, due to messaging delays, the headend cannot recover as fast as possible by making a repair at the point of failure.

Fast Reroute provides link protection to LSPs. This enables all traffic carried by LSPs that traverse a failed link to be rerouted around the failure. The reroute decision is completely controlled locally by the router interfacing the failed link. The headend of the tunnel is also notified of the link failure through the IGP or through RSVP; the headend then attempts to establish a new LSP that bypasses the failure.

Local reroute prevents any further packet loss caused by the failed link. This gives the headend of the tunnel time to re-establish the tunnel along a new, optimal route. If the headend still cannot find another path to take, it will continue using the backup tunnel.

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Figure 42 - TE FRR Example

The example in Figure 1 illustrates how Fast Reroute link protection is used to protect traffic carried in a TE tunnel between devices R1 and R9, as it traverses the mid-point link between devices R2 and R4. [The TE tunnel from R1 to R9 is considered to be the primary tunnel and is defined by labels 37, 14, and Pop.] To protect that R2-R4 link, you create a backup tunnel that runs from R2 to R4 by way of R6 and R7. This backup tunnel is defined by labels 17, 22, and Pop.

When R2 is notified that the link between it and R4 is no longer available, it simply forwards traffic destined for R4 through the backup tunnel. That is accomplished by pushing label 17 onto packets destined to R4 after the normal swap operation (which replaces label 37 with label 14) has been performed. Pushing label 17 onto packets forwards them along the backup tunnel, thereby routing traffic around the failed link. The decision to reroute packets from the primary tunnel to the backup tunnel is made solely by R2 upon detection of link failure.

The Fast Reroute feature has two noticeable benefits.

Increased reliability and minimal traffic loss it gives to IP traffic service during link loss.

37 17 22 14 None

R8

R2

R6

R4

R7

R1 R5

R9

PushPush 37

PopPop 22

SwapSwap 37->14PushPush 17

SwapSwap 17->22

PopPop 14

Label Stack: R1 R2 R6 R7 R4 R9

14 14

37 17 22 14 None

R8

R2

R6

R4

R7

R1 R5

R9

PushPush 37

PopPop 22

SwapSwap 37->14PushPush 17

SwapSwap 17->22

PopPop 14

Label Stack: R1 R2 R6 R7 R4 R9

14 14

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High scalability inherent in its design.

Increased Reliability for IP Services

MPLS traffic engineering with Fast Reroute uses fail over times that match the capabilities of SONET link restoration. This leverages a very high degree of resiliency for IP traffic that flows over a service provider's backbone, leading to more robust IP services and higher end-customer satisfaction.

High Scalability Solution

The Fast Reroute feature uses the highest degree of scalability by supporting the mapping of all primary tunnels that traverse a link onto a single backup tunnel. This capability bounds the growth of backup tunnels to the number of links in the backbone rather than the number of TE tunnels that run across the backbone.

TE/TE-FRR Design

Deciding on the tunnel topology and tunnel types

How to Route Traffic Into TE Tunnels

Policy Based Routing

You can use PBR to send traffic down a TE tunnel. However you cannot apply policy routing to an MPLS-VPN interface as the Hardware and IOS software for the VRF interface is not PBR aware. This enhancement may be added in future line cards and IOS software.

So for normal Ipv4 interface you just set the outgoing interface in the policy map as the tunnel interface.

RtrA(config)#int s0RtrA(config-if)#ip policy route-map set-tunnel

RtrA(config)#route-map set-tunnelRtrA(config-route-map)#match ip address 101RtrA(config-route-map)#set interface Tunnel1

Static Routing Into Tunnels

You can manually send traffic down specific TE tunnels using static routes. In this case the destination interface is the tunnel interface. This is the simplest method of “steering” traffic into a tunnel and many service providers use this method in relatively simple topologies.

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However this method is obviously un-scalable in larger, more complex topologies and can be prone to “routing loops” unless careful provisioning is adhered to.

An example syntax is:-

ip route H.H.H.H 255.255.255.255 Tunnel1 (where X.X.X.X is the I.P Destination)

Auto-Route

Cisco IOS MPLS Autoroute Announce installs the routes announced by the tail-end router and its downstream routers into the routing table (forwarding table) of the head-end router as directly reachable through the tunnel.

The Constrained Based Routing Algorithm allows MPLS TE to establish a Label Switch Path from the head-end to the tail-end node. By default, those paths will not be announced to the IGP routing protocol. Hence, any prefixes/networks announced by the tail end router and its downstream routers would not be "visible" through those paths.

For every MPLS TE tunnel configured with Autoroute Announce, the link state IGP will install the routes announced by the tail-end router and its downstream routers into the RIB. Therefore, all the traffic directed to prefixes topologically behind the tunnel head-end is pushed onto the tunnel.

To have a better understanding of this feature, consider an example with and without Autoroute Announce enabled.

Consider the topology of Figure 4. For the sake of simplicity, assume that Ri's loopback address is i.i.i.i.

Figure 43 - Topology Without Tunnels

The corresponding routing table on Router R1 with normal IGP and no MPLS TE looks like the following.

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Figure 44 - R1 Routing Table – No MPLS TE

Considering the same topology as in Figure 4, now let us introduce two MPLS Traffic Engineering tunnels T1 and T2 respectively. Tunnel T1 will originate in R1 and its tail end is R4. Tunnel T2 will originate in R1 and its tail end is R5.

MPLS TE Autoroute Announce will be enabled on the two tunnels. Similarly, R1 routing table entries are given in Figure 7.

Figure 45 – Topology With TE Tunnels

Figure 46 - R1 Routing Table With Autoroute Announce

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The routing tables (Figure 5 and Figure 7) demonstrate that R4 and R5 are directly reachable through tunnel T1 (resp. T2) with MPLS TE Autoroute Announce. Similarly, R8 is now reachable through the tunnel T1 via R4 instead of the "physical" connection.

Without Cisco MPLS TE Autoroute Announce, even though Tunnel T1 is up, route to R8 is done via the "physical" connection (as in Figure 5).

Forwarding Adjacency

The MPLS TE Forwarding Adjacency feature allows a network administrator to handle a traffic engineering, label-switched path (LSP) tunnel as a link in an Interior Gateway Protocol (IGP) network based on the Shortest Path First (SPF) algorithm. A forwarding adjacency can be created between routers regardless of their location in the network. The routers can be located multiple hops from each other, as shown in Figure 8.

Figure 47 - Forwarding Adjacency Topology

As a result, a TE tunnel is advertised as a link in an IGP network with the link's cost associated with it.

Routers outside of the TE domain see the TE tunnel and use it to compute the shortest path for routing traffic throughout the network.

Benefits

TE Tunnel Interfaces Advertised for SPF

TE tunnel interfaces are advertised in the IGP network just like any other links. Routers can then use these advertisements in their IGPs to compute the SPF even if they are not the head end of any TE tunnels.

Restrictions

Using the MPLS TE Forwarding Adjacency feature increases the size of the IGP database by advertising a TE tunnel as a link.

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The MPLS TE Forwarding Adjacency feature is supported by Intermediate System-to-Intermediate System (IS-IS). Open Shortest Path First (OSPF) support will be available in a future release.

When the MPLS TE Forwarding Adjacency feature is enabled on a TE tunnel, the link is advertised in the IGP network as a Type Length Value (TLV) 22 without any TE sub-TLV.

MPLS TE forwarding adjacency tunnels must be configured bidirectionally.

Do not use the tunnel mpls traffic-eng autoroute announce statement in your configuration when you are using forwarding adjacency.

Using Directed LDP Sessions

If you are using TE in conjunction with RFC2547 L3 VPN’s then an extra configuration step may be needed on the primary tunnel interface.

When the TE tunnel is terminated on the egress PE, the MPLS VPN and the TE work together without any additional configuration.

When the TE tunnel is terminated on any P routers (before the PE in the core), the MPLS VPN traffic forwarding fails because packets arrive with VPN labels as the outer labels, which are not in the LFIBs of these devices. Therefore, these intermediate routers are not able to forward packets to the final destination, the VPN customer network. In such a case, LDP/TDP should be enabled on the TE tunnel to solve the problem.

Below is an example of the extra configuration step required:-

P1#show run int tu0

interface Tunnel0 ip unnumbered Loopback0 no ip directed-broadcast ip route-cache distributed tag-switching ip *this enables tdp/ldp on the tunnel interface tunnel destination 10.5.5.5 tunnel mode mpls traffic-eng tunnel mpls traffic-eng autoroute announce tunnel mpls traffic-eng path-option 10 dynamic end

!

Number of Protected PrefixesIt is possible that if a customer has hundreds of prefixes in his FRR database that he may wish to prioritise which order prefixes get re-written. This way you can manually configure certain prefixes to be re-written on FRR switchover as a priority to ensure LSA’s are met.

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The MPLS TE—FRR Prefix Ordering Using an ACL feature allows you to prioritize the FRR database according to a single ACL ID. This feature was introduced in IOS 12.0(17)ST7.

The ACL ID can contain many networks and hosts. A match in the ACL simply gives precedence to the prefix and places this prefix earlier in the database to provide faster switchover time in the event of a failure.

Benefits

FRR Database Sorting. This feature adds a modified software sorting function for the FRR database based on the existence of a configured ACL. As a result, matching prefixes receive higher priority during a failure and fewer packets are lost.

Restrictions

This feature is limited to FRR functionality and the order of the failed-over routing prefixes.

This feature does not add, delete, or modify the routing prefixes in the FRR database; it just resorts them.

The following command output shows the FRR database before it is reordered:

Router# show mpls traffic-eng fast-reroute database

Tunnel head fast reroute information: Prefix Tunnel In-label Out intf/label FRR intf/label Status 10.0.6.1/32 Tu3 12307 PO1/0:Pop tag Tu10:tag-implicit ready 10.0.7.1/32 Tu3 12306 PO1/0:12305 Tu10:tag-implicit ready 10.0.8.1/32 Tu3 12304 PO1/0:12304 Tu10:tag-implicit ready 10.0.0.36/30 Tu3 12314 PO1/0:Pop tag Tu10:tag-implicit ready 10.0.0.40/30 Tu3 12312 PO1/0:Pop tag Tu10:tag-implicit ready 10.0.0.48/30 Tu3 12316 PO1/0:Pop tag Tu10:tag-implicit ready 10.0.0.52/30 Tu3 12317 PO1/0:12307 Tu10:tag-implicit ready 10.0.0.60/30 Tu3 12315 PO1/0:Pop tag Tu10:tag-implicit ready 10.0.0.64/30 Tu3 12318 PO1/0:12308 Tu10:tag-implicit ready

In the following command output, the last prefix, which is 10.0.0.64/30, is placed first in the FRR database:

Router# configure terminal

Router(config)# access-list 1 permit 10.0.0.64 0.0.0.3

In the following command output, the ACL is applied globally:

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Router(config)# mpls traffic-eng fast-reroute acl 1

In the following command output, the 10.0.0.64/30 prefix has been reordered and

now appears first in the FRR database:

Router# show mpls traffic-eng fast-reroute database

Tunnel head fast reroute information:Acl in use 1

Prefix Tunnel In-label Out intf/label FRR intf/label Status 10.0.0.64/30 Tu3 12318 PO1/0:12308 Tu10:tag-implicit ready 10.0.6.1/32 Tu3 12307 PO1/0:Pop tag Tu10:tag-implicit ready 10.0.7.1/32 Tu3 12306 PO1/0:12305 Tu10:tag-implicit ready 10.0.8.1/32 Tu3 12304 PO1/0:12304 Tu10:tag-implicit ready 10.0.0.36/30 Tu3 12314 PO1/0:Pop tag Tu10:tag-implicit ready 10.0.0.40/30 Tu3 12312 PO1/0:Pop tag Tu10:tag-implicit ready 10.0.0.48/30 Tu3 12316 PO1/0:Pop tag Tu10:tag-implicit ready 10.0.0.52/30 Tu3 12317 PO1/0:12307 Tu10:tag-implicit ready 10.0.0.60/30 Tu3 12315 PO1/0:Pop tag Tu10:tag-implicit ready LSP midpoint frr information: LSP identifier In-label Out intf/label FRR intf/label Status

“3” Implementation Of TE-FRR

“3” Network Architecture

Introduction

The core network of “3” is illustrated in Figure 9 below. It consists of 3 major POP’s deployed in major cities within the U.K.

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Figure 48 - "3" Core Network Architecture

The core network is built entirely out of 124XX routers with 7200’s used as Route Reflectors. The network utilises MPLS-VPN L3 RFC2547.

Cisco 12416’s are used as core switching routers and interface to a Nortel Optera DWDM network for Optical Transport. OC-192 POS linecards are used to buid a 10G network infrastructure and these nodes are used as “P” devices in the context of the MPLS-VPN.

Cisco 12410’s are used as edge routers (PE) and are inter-connected via OC-48 POS lincards to the P routers within the POP. VPN interface’s are present on the GigE cards within these routers. Initially Trident (3 X GigE) linecards were used and later these were swapped out for the new Tango (10 X GigE) linecards.

The design uses a wide range of PE-CE connection models for various VPN’s:-

Static

Connected

OSPF

TE-FRR Design

In the design it was decided to only protect the core OC-192 POS (Inter-POP) links as these had the greatest chance of failure compared to the Intra-POP links. Obviously TE-FRR provides a very cost effective mechanism of link protection compared to Sonet APS.

In the design IP traffic will be protected in the core by Fast Re-Route (FRR) for link protection for sub 50ms performance. Tunnel Engineering aims to optimize network resource usage by directing traffic onto LSP tunnels established according to criteria other than lowest cost or fewest hops, which existing routing protocols use today. For example, to minimize congestion and maximize performance, an ISP might want all traffic destined for a particular network to use the path with maximum bandwidth.

Fast restoration is possible within 50 milliseconds. This is because no signaling is required, the backup tunnel is already in place, and the ingress to the back-up tunnel can be co-located on the device that detects the failure. Protection and restoration span is flexible. Backup LSP tunnels can be set up to protect individual links.

MPLS-TE FRR will be used to protect all the OC-192 POS links between the 3 x GSRs in the test network. In the event of a link failure, the backup FRR tunnels will provide an immediate local path around the failure until the primary tunnel has re-optimised.

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Primary Tunnels

So in the design we have a number of 1-Hop Primary tunnels going between the POP’s. This makes a total of 6 Primary tunnels in the design. The primary tunnels are dynamically routed to the TE loopback address of its neighbouring 2 POP’s.

Initially auto-route was used as the mechanism for injecting traffic into the tunnels, however this was replaced with “Forwarding Adjacency” during system testing dues to un-expected traffic loss. (See Sec XXX)

Its important to note that because of the use of 1-Hop tunnels that the tunnel head end is also the point of local repair (PLR) so after an FRR operation the primary tunnel will re-route across the 2-Hop link. This will happen after the fast re-write operation.

Backup Tunnels

So each protected link has a 2-Hop backup tunnel provisioned as the alternate path when FRR-LP kicks in. Each backup tunnel is explicitly configured to go via the alternate POP to reach the original POP destination. Figure 10 gives an example of the tunnel provisioning.

Obviously explicit backup tunnel configuration is sensible as you obviously provision the backup tunnels to cross a specific 2 hop path

Figure 49 - Illustration of Primary and Backup TE Tunnels

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i.p addresses

Source Router

Description Tunnel Number

Explicit/ Dynamic

Final Destination

GSR1 Primary 1-2 1 Dynamic GSR2


GSR1 Backup of 1-2 11 Explicit via GSR3 GSR2










Table 9 Tunnel Provisioning

All Primary TE tunnel parameters will be as follows:

· IP Unnumbered to Loopback 0

· Path option - Dynamic

· Autoroute announce

· Priority 5 5

· Bandwidth 1

· Fast Re-Route enabled

All FRR backup TE tunnel parameters will be as follows:

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· IP Unnumbered to Loopback 0

· Path option - Explicit path

· Priority 0 0

· Bandwidth 0

POS interface specifics:

· Enable AIS alarm when interface shutdown

· IP RSVP bandwidth to match link speed

Sample configurations

Generic Global Commands

mpls traffic-eng tunnels

no tag-switching ip propagate-ttl forwarded

tag-switching tdp router-id Loopback0

router isis

passive-interface Loopback0

mpls traffic-eng router-id Loopback0

mpls traffic-eng level-2

net 49.4401.1720.3125.0254.00

is-type level-2-only

domain-password vlPhuj8p5

metric-style wide level-2

max-lsp-lifetime 65535

lsp-refresh-interval 65000

no hello padding

log-adjacency-changes

Birmingham P Router

interface Tunnel1001

description from bm0gsr01 tunnel1001 to hh0gsr01 tunnel1002, Primary

ip unnumbered Loopback0

no ip directed-broadcast

mpls label protocol tdp

tag-switching ip

110

tunnel destination 172.31.252.254

tunnel mode mpls traffic-eng

tunnel mpls traffic-eng autoroute announce

tunnel mpls traffic-eng forwarding-adjacency

tunnel mpls traffic-eng priority 5 5

tunnel mpls traffic-eng bandwidth 1

tunnel mpls traffic-eng path-option 1 dynamic

tunnel mpls traffic-eng record-route

tunnel mpls traffic-eng fast-reroute


description from bmgsr01 tunnel1002 to mr0gsr01 tunnel1002, Primary




tag-switching ip



tunnel mpls traffic-eng autoroute announce

tunnel mpls traffic-eng forwarding-adjacency


tunnel mpls traffic-eng bandwidth 1

tunnel mpls traffic-eng path-option 1 dynamic


tunnel mpls traffic-eng fast-reroute

!


description from bm0gsr01 tunnel2001 via mr0gsr01 to hh0gsr01 tunnel2002, Backup of pos3/0






tunnel mpls traffic-eng path-option 1 explicit name backup-to-hh01-via-mr01


!


description from bm0gsr01 tunnel2002 via hh0gsr01 to mr0gsr01 tunnel2002, Backup of pos12/0





111


tunnel mpls traffic-eng path-option 1 explicit name backup-to-mr01-via-hh01


interface POS3/0

description from bm0gsr01 pos 3/0 to hh0gsr01 pos 12/0 STM-64

ip address 172.31.254.6 255.255.255.252


no ip proxy-arp

ip router isis

encapsulation ppp

carrier-delay msec 0



mpls traffic-eng backup-path Tunnel2001

tag-switching ip

no peer neighbor-route

crc 32

clock source internal

pos ais-shut

pos framing sdh

pos report lrdi

pos flag s1s0 2

tx-cos STM64-TX

no cdp enable

isis circuit-type level-2-only

isis metric 100 level-2

isis password vlPhuj8p5 level-2

ip rsvp bandwidth 10000000 10000000

interface POS12/0

description from bm0gsr01 pos 12/0 to mr0gsr01 pos 12/0 STM-64

ip address 172.31.254.17 255.255.255.252


no ip proxy-arp

ip router isis

encapsulation ppp

carrier-delay msec 0



mpls traffic-eng backup-path Tunnel2002

tag-switching ip

112

no peer neighbor-route

crc 32

clock source internal

pos ais-shut

pos framing sdh

pos report lrdi

pos flag s1s0 2

tx-cos STM64-TX

no cdp enable

isis circuit-type level-2-only

isis metric 100 level-2

isis password vlPhuj8p5 level-2

ip rsvp bandwidth 10000000 10000000

ip explicit-path name backup-to-hh01-via-mr01 enable

next-address 172.31.254.18


!

ip explicit-path name backup-to-mr01-via-hh01 enable



The configurations are in principle identical for Hemel and Manchester apart from the I.P addresses.

Quality of Service

Introduction

In order to fulfil ST requirements of having four distinct classes of service, each with their specific service characteristics, QoS mechanisms are deployed on the access layer and backbone links. The following section describes the technical implementation and features that form the basis for a set of new innovative products.

Scalability and stability are the main criteria for any extension of the network. It is absolutely necessary to aggregate IP streams with identical flow characteristic. The expression used for this solution is “service classes”. Dedicated handling of single streams is only meaningful in special cases when high bandwidths are involved, and there are no plans for this solution to be introduced in the first instance.

The number of service classes should be strictly limited from the technical point of view. This is not a restriction to construct various commercial products on top of it. Service level agreements (SLA) form the definition interface for the service that will be delivered to the customer by ST. Parameters should describe a probability for a certain service and will be reported on a per class base.

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For ST MPLS backbone network a robust solution that aligns to base ideas of IETF's DiffServ approach would appear to be practicable at present. With respect to the intended MPLS solution, a maximum of 8 code points per path can be supported. These are distinguished using the three experimental bits of the MPLS shim header. A large part of best effort background traffic is required to produce efficient high quality service classes because DiffServ is based on relative priorities. The strength of a large IP backbone network is to be seen in the fact that high-priority and low-priority traffic is merged on a single network platform. This results in synergy that permits optimum resource utilisation. The bundling of many different traffic streams (statistical multiplexing) smoothes individual bursts.

Differentiated Services Model – Introduction

This section is intended as an introduction to the Differentiated Services (DiffServ) reference model.

DiffServ is a new model by which traffic is treated by intermediate systems with relative priorities based on the type of services (ToS) or Differentiated Services Code Point (DSCP) field. Defined in RFC’s 2474 and 2475, the DiffServ standard supersedes the original specification for defining packet priority described in RFC 791.

The new DiffServ standard proposes a new way of interpreting a field that has always been part of an IP packet. In the DiffServ standard, the ToS field will be renamed to Differentiated Services Code Point (DSCP) and will have new meaning. The DiffServ standard proposes to increase the number of definable priority levels by re-allocating bits of an IP packet for priority marking.

As per RFC 791, the ToS field describes one entire byte (eight bits) of an IP packet. Precedence refers to the three most significant bits of the ToS field---that is, [XXX]XXXXX. There may be some confusion because the RFC 1349 defines a new 4-bit ToS XXX[XXXX]X as shown on the following picture.

114

Figure 50 Various interpretations of the TOS field

The three most significant bits of the RFC-791 ToS field - the precedence bits - define the IP packet priority or importance.

XXX00000 Bits 0,1,2 = Precedence, where:

111 = Network Control = Precedence 7

110 = Internetwork Control = Precedence 6

101 = CRITIC/ECP = Precedence 5

100 = Flash Override = Precedence 4

011 = Flash = Precedence 3

010 = Immediate = Precedence 2

001 = Priority = Precedence 1

000 = Routine = Precedence 0

The four bits of the RFC-1349 TOS are used in IOS configuration and have the following semantics:

000XXXX0 Bits 3, 4, 5, 6:

1000 = Minimize delay

0100 = Maximize throughput

0010 = Maximize reliability

0001 = Minimize monetary cost

0000 = Normal service

0000000X Bit 7: Reserved for future use

This one-byte ToS field has been almost completely unused since it was proposed almost 20 years ago. Only in the last few years have Cisco and other router companies begun utilising the Precedence bits for making forwarding decisions.

The DiffServ standard follows a similar scheme to RFC 791, but utilises more bits for setting priority. The new standard maintains backward compatibility with RFC 791 implementations, but allows more efficient use of bits 3, 4, and 5. (Bits 6 and 7 will still be reserved for future development.) With the additional 3 bits, there are now a total of 64 classes instead of the previous 7 classes.

115

RFC 2475 defines Per Hop Behaviour (PHB) as the externally observable forwarding behaviour applied at a DiffServ-compliant node to a DiffServ Behaviour Aggregate (BA).

With the ability of the system to mark packets according to DSCP setting, collections of packets with the same DSCP setting and sent in a particular direction can be grouped into a BA. Packets from multiple sources or applications can belong to the same BA.

In other words, a PHB refers to the packet scheduling, queuing, policing, or shaping behaviour of a node on any given packet belonging to a BA, as configured by a service level agreement (SLA) or a policy map.

The following sections describe the four available standard PHBs:

Default PHB (as defined in RFC 2474)

Class-Selector PHB (as defined in RFC 2474)

Assured Forwarding (AFxy) PHB (as defined in RFC 2597)

Expedited Forwarding (EF) PHB (as defined in RFC 2598)

Default PHB

The default PHB essentially specifies that a packet marked with a DSCP value of 000000 (recommended) receives the traditional best-effort service from a DS-compliant node (that is, a network node that complies with all of the core DiffServ requirements). Also, if a packet arrives at a DS-compliant node, and the DSCP value is not mapped to any other PHB, the packet will get mapped to the default PHB.

For more information about default PHB, refer to RFC 2474, Definition of the Differentiated Services Field in IPv4 and IPv6 Headers.

Class-Selector PHB:

To preserve backward-compatibility with any IP Precedence scheme currently in use on the network, DiffServ has defined a DSCP value in the form xxx000, where x is either 0 or 1. These DSCP values are called Class-Selector Code Points. (The DSCP value for a packet with default PHB 000000 is also called the Class-Selector Code Point.)

The PHB associated with a Class-Selector Code Point is a Class-Selector PHB. These Class-Selector PHBs retain most of the forwarding behaviour as nodes that implement IP Precedence-based classification and forwarding.

For example, packets with a DSCP value of 110000 (the equivalent of the IP Precedence-based value of 110) have preferential forwarding treatment (for scheduling, queuing, and so on), as compared to packets with a DSCP value of 100000 (the equivalent of the IP Precedence-based value of 100). These Class-Selector PHBs ensure that DS-compliant nodes can coexist with IP Precedence-based nodes.

The DiffServ standard utilises the same precedence bits (the most significant bits: 0, 1, and 2) for priority setting, but further clarifies their functions/definitions, plus offers finer priority granularity through use of the next three bits in the ToS field. DiffServ reorganises (and renames) the precedence levels (still defined by the three most significant bits of the ToS field) into the following categories:

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Table 10 Class-Selector PHBs

Precedence 7 Stays the same (link layer and routing protocol keep alive)

Precedence 6 Stays the same (used for IP routing protocols)

Precedence 5 Class 5





Precedence 0 Best effort

For more information about class-selector PHB, refer to RFC 2474, Definition of the Differentiated Services Field in IPv4 and IPv6 Headers.

Assured Forwarding PHB

Assured Forwarding PHB is nearly equivalent to Controlled Load Service available in the integrated services model. AFxy PHB defines a method by which BAs can be given different forwarding assurances.

For example, network traffic can be divided into the following classes:

Gold: Traffic in this category is allocated 50 percent of the available bandwidth.

Silver: Traffic in this category is allocated 30 percent of the available bandwidth.

Bronze: Traffic in this category is allocated 20 percent of the available bandwidth.

Further, the AFxy PHB defines four AF classes: AF1, AF2, AF3, and AF4. Each class is assigned a specific amount of buffer space and interface bandwidth, according to the SLA with the service provider or policy map.

Within each AF class, you can specify three drop precedence (dP) values: 1, 2, and 3. Assured Forwarding PHB can be expressed as shown in the following example:

AFxy

In this example, x represents the AF class number (1, 2, or 3) and y represents the dP value (1, 2, or 3) within the AFx class. In instances of network traffic congestion, if packets in a particular AF class (for example, AF1) need to be dropped, packets in the AF1 class will be dropped according to the following guideline:

dP(AFx1) <= dP(AFx2) <= dP(AFx3)

where dP (AFxy) is the probability that packets of the AFxy class will be dropped. In other words, y denotes the dP within an Afx class. The dP method penalises traffic flows within a particular BA that exceed the assigned bandwidth. Packets on these offending flows could be re-marked by a policer to a higher drop precedence.

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Bits 3 and 4 of DiffServ field allow further priority granularity through the specification of a packet drop probability for any of the defined classes. Collectively, Classes 1-4 are referred to as Assured Forwarding (AF). The following table illustrates the DSCP coding for specifying the priority level (class) plus the drop percentage. (Bits 0, 1, and 2 define the class; bits 3 and 4 specify the drop percentage; bit 5 is always 0.)

Using this system, a device would first prioritise traffic by class, then differentiate and prioritise same-class traffic by considering the drop percentage. It is important to note that this standard has not specified a precise definition of "low," "medium," and "high" drop percentages. Additionally, not all devices will recognise the DiffServ bit 3 and 4 settings. Remember also that even when the settings are recognised, they do not necessarily trigger the same forwarding action to be taken by each type of device on the network---each device will implement its own response in relation to the packet priorities it detects. The DiffServ standard is meant to allow a finer granularity of priority setting for the applications and devices that can make use of it, but it does not specify interpretation (that is, action to be taken).

Expedited Forwarding PHB

Resource Reservation Protocol (RSVP), a component of the integrated services model, provides a Guaranteed Bandwidth Service. Applications such as Voice over IP (VoIP), video, and online trading programs require this kind of robust service. The EF PHB, a key ingredient of DiffServ, supplies this kind of robust service by providing low loss, low latency, low jitter, and assured bandwidth service.

EF PHB is ideally suited for applications such as VoIP that require low bandwidth, guaranteed bandwidth, low delay, and low jitter. The recommended DSCP value for EF PHB is 101110.

For more information about EF PHB, refer to RFC 2598, An Expedited Forwarding PHB.

Figure 51 DSCP Interpretation

Class 0

Prec 0

Class 1

Prec 1

Class 2

Prec 2

Class 3

Prec 3

Class 4

Prec 4

Reserved

Prec 5

Routing

Prec 6

Routing

Prec 7

Class-Selector PHBs 000 000

BE PHB

DSCP 0

001 000

CS PHB

DSCP 8

010 000

CS PHB

DSCP 16

011 000

CS PHB

DSCP 24

100 000

CS PHB

DSCP 32

101 000

CS PHB

DSCP 40

110 000

CS PHB

DSCP 48

111 000

CS PHB

DSCP 56

Unused 000 001 001 001 010 001 011 001 100 001 101 001 110 001 111 001

Low Drop Precedence 000 010 001 010

AF11

DSCP 10

010 010

AF21

DSCP 18

011 010

AF31

DSCP 26

100 010

AF41

DSCP 34

101 010 110 010 111 010

Unused 000 011 001 011 010 011 011 011 100 011 101 011 110 011 111 011

Medium Drop Precedence

000 100 001 100

AF12

DSCP 12

010 100

AF22

DSCP 20

011 100

AF32

DSCP 28

100 100

AF42

DSCP 36

101 100 110 100 111 100

Unused 000 101 001 101 010 101 011 101 100 101 101 101 110 101 111 101

High Drop 000 110 001 110 010 110 011 110 100 110 101 110 110 110 111 110

118

Precedence AF13

DSCP 14

AF23

DSCP 22

AF33

DSCP 30

AF43

DSCP 38

EF PHB

DSCP 46

Unused 000 111 001 111 010 111 011 111 100 111 101 111 110 111 111 111

QoS and VoIP

Voice quality is directly affected by two major factors:

Lost packets

Delayed packets

Packet loss causes voice clipping and skips. The industry standard codec algorithms used in Cisco Digital Signal Processor (DSP) can correct for up to 30 ms of lost voice. Cisco Voice over IP (VoIP) technology uses 20-ms samples of voice payload per VoIP packet. Therefore, for the codec correction algorithms to be effective, only a single packet can be lost during any given time.

Packet delay can cause either voice quality degradation due to the end-to-end voice latency or packet loss if the delay is variable. If the end-to-end voice latency becomes too long (250 ms, for example), the conversation begins to sound like two parties talking on a CB radio. If the delay is variable, there is a risk of jitter buffer overruns at the receiving end. Eliminating drops and delays is even more imperative when including fax and modem traffic over IP networks. If packets are lost during fax or modem transmissions, the modems are forced to "retrain" to synchronize again. By examining the causes of packet loss and delay, we can gain an understanding of why Quality of Service (QoS) is needed.

Network congestion can lead to both packet drops and variable packet delays. Voice packet drops from network congestion are usually caused by full transmit buffers on the egress interfaces somewhere in the network. As links or connections approach 100% utilization, the queues servicing those connections become full. When a queue is full, new packets attempting to enter the queue are discarded.

Because network congestion is typically sporadic, delays from congestion tend to be variable in nature. Egress interface queue wait times or large serialization delays cause variable delays of this type. Both of these factors are discussed in the next section, "Delay and Jitter".

Delay is the time it takes for a packet to reach the receiving endpoint after being transmitted from the sending endpoint. This time is termed the "end-to-end delay” and it consists of two components: fixed network delay and variable network delay. Jitter is the delta, or difference, in the total end-to-end delay values of two voice packets in the voice flow.

Fixed network delay should be examined during the initial design of the VoIP network. The International Telecommunications Union (ITU) standard G.114 states that a one-way delay budget of 150 ms is acceptable for high voice quality. Research at Cisco has shown that there is a negligible difference in voice quality scores using networks built with 200-ms delay budgets. Examples of fixed network delay include the propagation delay of signals between the sending and receiving endpoints, voice encoding delay, and the voice packetization time for various VoIP codecs. Propagation delay calculations work out to almost 0.0063 ms/km. The G.729A codec, for example, has a 25 ms encoding delay value (two 10 ms frames + 5 ms look-ahead) and an additional 20 ms of packetization delay.

Congested egress queues and serialization delays on network interfaces can cause variable packet delays. Without Priority or Low-Latency Queuing (LLQ), queuing delay times equal serialization delay times as

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link utilization approaches 100%. Serialization delay is a constant function of link speed and packet size. As shown in Table 11, the larger the packet and the slower the link clocking speed, the greater the serialization delay. While this is a known ratio, it can be considered variable because a larger data packet can enter the egress queue before a voice packet at any time.

If the voice packet must wait for the data packet to serialize, the delay incurred by the voice packet is its own serialization delay plus the serialization delay of the data packet in front of it. Using Link Fragmentation and Interleave (LFI) techniques, serialization delay can be configured to be a constant delay value.

Table 11 Serialisation delay [ms] as function of link speed and packet size

Link speed \ packet size 64 bytes 128 bytes 256 bytes 512 bytes 1024 bytes 1500 bytes

56 kbps 9 18 36 72 144 214

64 kbps 8 16 32 64 128 187

128 kbps 4 8 16 32 64 93

256 kbps 2 4 8 16 32 46

512 kbps 1 2 4 8 16 23

2048 kbps (E1) 0,25 0,5 1 2 4 5,8

34 Mbps (E3) 0,015 0,3 0,06 0,12 0,24 0,35

155 Mbps (STM-1) 3.3*10-3 0,006 0,013 0,026 0,052 0,077

622 Mbps (STM-4) 0,82*10-3 1,6*10-3 3,3*10-3 6,6*10-3 0,013 0,019

2.5 Gbps (STM-16) 0,2*10-3 0,4*10-3 0,82*10-3 1,6*10-3 3,3*10-3 4,8*10-3

Because network congestion can be encountered at any time within a network, buffers can fill instantaneously. This instantaneous buffer utilization can lead to a difference in delay times between packets in the same voice stream. This difference, called jitter, is the variation between when a packet is expected to arrive and when it actually is received. To compensate for these delay variations between voice packets in a conversation, VoIP endpoints use jitter buffers to turn the delay variations into a constant value so that voice can be played out smoothly.

Cisco VoIP endpoints use DSP algorithms that have an adaptive jitter buffer between 20 and 50 ms, as illustrated in the following picture. The actual size of the buffer varies between 20 and 50 ms based on the expected voice packet network delay. These algorithms examine the timestamps in the Real-time Transport Protocol (RTP) header of the voice packets, calculate the expected delay, and adjust the jitter buffer size accordingly. When this adaptive jitter buffer is configured, a 10-ms portion of "extra" buffer is configured for variable packet delays. For example, if a stream of packets is entering the jitter buffer with RTP timestamps indicating 23 ms of encountered network jitter, the receiving VoIP jitter buffer is sized at a maximum of 33 ms. If a packet's jitter is greater than 10 ms above the expected 23-ms delay variation (23 + 10 = 33 ms of dynamically allocated adaptive jitter buffer space), the packet is dropped.

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Figure 52 Adaptive jitter buffer

Voice quality is only as good as the quality of the weakest network link. Packet loss, delay, and delay variation all contribute to degraded voice quality. In addition, because network congestion (or more accurately, instantaneous buffer congestion) can occur at any time in any portion of the network, network quality is an end-to-end design issue.

Call admission control is another important issue that needs to be considered. Call admission control is a mechanism for ensuring that voice flows do not exceed the maximum provisioned bandwidth allocated for voice conversations. After doing the calculations to provision the network with the required bandwidth to support voice, data, and possibly video applications, it is important to ensure that voice does not oversubscribe the portion of the bandwidth allocated to it. While most QoS mechanisms are used to protect voice from data, call admission control is used to protect voice from voice. This is illustrated in the following figure, which shows an environment where the network has been provisioned to support two concurrent voice calls. If a third voice call is allowed to proceed, the quality of all three calls is degraded. Call admission control should be external to the network.

Figure 53 - Call admission control

Interleaving mechanisms: FRF.12 or MLPPP / LFI

For low-speed WAN connections (in practice, those with a clocking speed of 1 Mbps or below), it is necessary to provide a mechanism for Link Fragmentation and Interleaving (LFI). A data frame can be sent to the physical wire only at the serialization rate of the interface. This serialization rate is the size of the frame divided by the clocking speed of the interface. For example, a 1500-byte frame takes 214 ms to serialize on a 56-kbps circuit. If a delay-sensitive voice packet is behind a large data packet in the egress interface queue, the end-to-end delay budget of 150-200 ms could be exceeded. In addition, even relatively small frames can adversely affect overall voice quality by simply increasing the jitter to a value greater than the size of the adaptive jitter buffer at the receiver.

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LFI tools are used to fragment large data frames into regularly sized pieces and to interleave voice frames into the flow so that the end-to-end delay can be predicted accurately. This places bounds on jitter by preventing voice traffic from being delayed behind large data frames, as illustrated in the following figure. The two techniques used for this are FRF.12 for Frame Relay and Multilink Point-to-Point Protocol (MLPPP) for point-to-point serial links.

Figure 54 LFI to reduce frame delay and jitter

A 10-ms blocking delay is the recommended target to use for setting fragmentation size. To calculate the recommended fragment size, divide the recommended 10 ms of delay by one byte of traffic at the provisioned line clocking speed, as follows:

Fragment_Size = (Max_Allowed_Jitter * Link_Speed_in_kbps) / 8

For example:

Fragment_Size = (10 ms * 56) / 8 = 70 bytes

The following table shows the recommended fragment size for various link speeds.

Table 12 Recommended fragment size

Link Speed

(kbps)

Recommended fragment size

(bytes)

56 70

64 80

128 160

256 620

512 640

768 960

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Obviously, the fragmentation size should be set larger than the largest VoIP packet in order to ensure that no VoIP packets get fragmented.

When using FRF.12 as an LFI mechanism on a Frame Relay access link, traffic shaping (either FRTS or dTS) becomes mandatory. Enabling FRF.12 will have an impact on the FRTS / dTS shaping parameters, since it adds 4 bytes of overhead to each fragment (2 bytes of FRF.12 overhead and 2 bytes of Cisco encapsulation overhead). The FRTS implementation will take into account this additional overhead (but still not the FCS and flag overhead) but the dTS overhead will not take into account the additional FRF.12 / Cisco encapsulation overhead). This is because FRF.12 runs in distributed mode on the VIP (dFRF.12).

Delay Model

The delay model for an IP packet consists of the summary of individual delays of nodes and links that are part of the end-to-end connection. The main factors that determine the overall end-to-end delay are typically:

Serialisation delay of narrow-band links

Propagation delays of long distance connections

Queuing delay in case of congestion situations

All times have to be described statistically, and must be seen as average in a certain time period.

Table 13 The components of the end-to-end delay model

Decision Delay

TDecision

This is the required time in a node to decide what interface a packet should go out. There can be a dependence on node utilisation, but in general on the high-end platforms TDecision < 1ms.

Queuing Delay

TQueuing

Queuing delay has variable dependencies to determine this delay, queue length, queuing mechanism, line utilisation, platform and CPU utilisation.

During times of non-congestion, there is no queuing delay; once congestion occurs the extra CPU cycles required to manage the scheduling has a small impact on the delay variable in the network.

Serialisation Delay

TSerialisation

This is the time that is necessary to put a packet of a certain size on a line of a certain speed (please see the Table 11)

Transmit Buffer Delay

TTransmit

On the egress interface a single buffer exist which additionally has an influence on the transmit delay. This buffer is used to control the various queuing mechanisms (CBWFQ/MDRR) in front of the transmit queue, by using a threshold. The length of this queue can be configured. A suited set-up has to be decided upon to minimise delay and maximise efficiency.

Propagation Delay

TPropagation

Describes the speed of light in a fibre which is about 6 ms per 1000 Km (2/3 c0)

Node Delay

TNode

The node delay summarises all node dependent delays per node.

Link Delay

TLink

The link delay summarises all link dependent delays per link.

Core Delay

TCore

The core delay summarises all core dependent delays, which are all node and link delays inside the core. This includes PE routers, P routers and the links in-between. Summarizing node and link delay for the core simplifies the delay model.

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Access Delay

TAccess

The access delay summarises all access dependent delays, which are all node and link delays in the access network. This includes CE routers, PE routers and the links in-between. Summarizing node and link delay for the access network simplifies the delay model.

End-to-End Delay

TEnd-to-End

The end-to-end delay is defined by the following formula:

Figure 55 Overview of end-to-end delay segments.

QoS in an MPLS network

MPLS is a technology allowing multi-service networking in an IP environment. In MPLS packets QoS information is carried in the EXP bits of the MPLS header of frame based MPLS packets. The MPLS EXP bits are only three bits long, while the DSCP bits are six. Therefore not all the information is copied directly from the DSCP IP field into the MPLS EXP field. Only the class selector (three most significant bits) are copied into the MPLS EXP bits by default as demonstrated in the following figure.

CE PE P P PE CE

Tnode Tlink

Tdecission Tqueueing Ttransmit Tserialization Tpropagation

Taccess TaccessTcore

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Figure 56 DSCP to EXP mapping

demonstrates the DSCP/EXP location; the MPLS header is pre-pended to the front of the IP packet. It is also feasible that multiple labels are added to the front of the IP packets instead of the one demonstrated in the drawing (e.g. MPLS/VPN label, TE label, FRR label). In such case, the QoS features in MPLS core devices shall only look in the EXP bits of the top-most label as the DSCP and “inner” labels in the label stack may carry customer-defined classes of services.

Figure 57 DSCP / MPLS Headers

IPv4 Packet IPv4 Packet Label x

DSCPabcd

DSCPabcd

EXPab

IPv4 Dom ain MPLS Dom ain

DiffServ Aware TE

ST QoS design – An Overview

The following table and figure give an overview of the various QoS mechanisms that are used in the ST MPLS network

The various QoS mechanisms and their detailed configuration will be discussed in detail in the subsequent sections. Detailed configuration templates will be derived during staging procedures. It should be understood that the IP addresses, DLCI numbers, VPI / VCI numbers, ACL numbers, etc, have been taken for the sake of examples and should be adapted to the specific requirements of the ST network.

It is Cisco’s experience that a Quality of Service design and deployment is never a straightforward process – after an initial deployment, a performance assessment phase and subsequent tuning of the QoS

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deployment is a necessity. Therefore, we strongly recommend a tuning phase while beta customers are connected.

Table 14 CoS Mechanisms Overview

Marketintg

Class

QoS

Mechanism

Standard

Best Effort data

(e.g. http)

Business

Business data

(e.g. SNA)

Streaming

Multimedia

(e.g. Video)

Voice

VoIP

Routing

updates

Management

(e.g. SNMP)

PHB

DSCP

EXP

BE

0

0

AF11

10

1

AF31

26

3

EF

46

5

CS5

48

6

CS6

48

6

Max. % of link BW 25% 25% 25% 25% - -

Queue Length long medium short very short medium medium

Classification CE any non-classified packet ACL 100 ACL 101 ACL 102 - ACL 103

PE DSCP DSCP DSCP DSCP - ACL 103

P EXP EXP EXP EXP - -

Marking CE MQCLI MQCLI MQCLI MQCLI - LPR

PE - - - - - LPR

P - - - - - -

Policing CE - MQCLI MQCLI MQCLI - MQCLI

P/PE - - - - - -

Class Queuing Access class-default business streaming voice (LLQ) mgmt mgmt

Core class-default business streaming voice (LLQ) business business

Congestion

Avoidance

CE,PE DSCP WRED DSCP WRED DSCP WRED Tail drop DSCP WRED DSCP WRED

P EXP WRED EXP WRED EXP WRED Tail drop

(minTH=maxTH)

EXP WRED EXP WRED

The drawing below displays an overview of QoS mechanisms used in the ST network. The following chapters will detail the QoS design on a hop-by-hop basis, following the packet from source (left CE) to its destination (right CE).

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Figure 58 QoS mechanisms overview

CE-to-PE QoS mechanisms (applied on the CE) – PPP or HDLC

Classification

On the CE, packets will be classified with extended access lists (ACLs). These ACLs can match packets on IP S/D address, protocol type, and UDP/TCP port numbers.

The ACLs for Business (100) Streaming (101) and Voice (102) traffic should be agreed with the customer. Any non-classified traffic will go into Standard traffic class, which is implemented as class-default in MQC defintion.

The following is an example ACL for Voice traffic:

!! Voice!access-list 102 permit udp any any range 16384 32767!! Voice Signalling MGCP!access-list 102 permit udp any any eq 2427access-list 102 permit tcp any any eq 2428access-list 102 permit tcp any any eq 1720!! H.323 voice control traffic!access-list 102 permit tcp any any range 11000 11999!

MPLS

IP IP

GSRP

MDRRWRED

MDRRWRED

10k,7206VXR

PE

N/A

LLQ

WR

ED

10k,7206 VXR

PE

N/A

LLQWRED

Managed CEN

/ALL

QW

RE

DManaged CE

N/A

N/A

LAN

MPLS

LAN

Classification (ACL)Marking (CAR, DSCP)

Policing (MQCLI)Queuing (DSCP)

Cong. mgmt. (DSCP)

Classification (QoS-group)Marking (DSCP->EXP auto)

Queuing (DSCP)Cong. mgmt. (DSCP)

Classification (DSCP)Queuing (DSCP)Cong. mgmt. (DSCP)

Classification (EXP)Queuing (EXP MDRR)

Cong. mgmt (EXP)[to-fabric, to-interface]

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The ACL for Management (103) traffic should match SNMP, TFTP, TELNET and any other required traffic to and from the network management systems IP address range.

!access-list 103 permit tcp any any eq bgpaccess-list 103 permit udp any any eq ripaccess-list 103 permit tcp any <NOC_lan> eq telnetaccess-list 103 permit udp any <NOC_lan> eq snmpaccess-list 103 permit udp any <NOC_lan> eq tftp

!

Voice signalling traffic will need to be classified and marked appropriately. Depending on the customer VoIP implementation, the different possibilities are:

RTCP: odd RTP port numbers

H.323 / H.245 standard connect: TCP 11xxx

H.323 / H.245 fast connect: TCP 1720

H.323 / H.225 RAS: TCP 1719

Skinny control traffic: TCP 2000-2002

ICCP: TCP 8001-8002

MGCP: UDP 2427, TCP 2428

Dependent on the actual signalling method used (packet sizes), speed of the access links and the number of concurrent voice call set-ups that need to be supported, two possible design options can be taken with regards to the queuing method used.

Queue the voice signalling packets in the same PQ as the actual voice bearer packets. This will result in a simpler design but could delay the transmission of some of the voice bearer packets (dependent on voice signalling packet size, access link speed and number of concurrent voice call set-ups). This could than have an impact on the voice delay / jitter.

Queue the voice signalling packets in another normal class queue. This should ideally be a separate class queue from the ones that are used for regular data traffic to ensure delivery of the voice signalling packets. This will result in a more complicated design where bandwidth needs to be allocated for the voice signalling class. Also, voice signalling packets might be delayed through the network resulting in a delay in the voice call set-up process. The advantage is that the actual voice quality will not be impacted as no voice signalling packets will travel in the PQ.

Testing has indicated that, without cRTP (Compressed Real Time Protocol) enabled, the effect of mapping VoIP signalling packets together with the VoIP bearer packets in the same priority queue is negligible. The signalling packets have little effect on the latency nor do they cause any drops due to the default bust size of 200ms that has been built into the priority queue. Therefore, the design recommendation is to match the VoIP signalling packets with ACL 102 and queue them together with the VoIP bearer packets in the priority queue.

It should however be understood that VoIP signalling implementations differ and that some might have a negative effect on the performance of the priority queue. In that event, the VoIP signalling traffic needs to be mapped in another class queue (Business, for example).

The classified traffic will subsequently be mapped in their respective classes using the MQCLI. The Standard traffic will not match any of the classes and will be mapped in the default class (class-default). A maximum of 64 classes can be defined on a single router.

!

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class-map match-all business match access-group 100class-map match-all streaming match access-group 101class-map match-all voice match access-group 102class-map match-any management match access-group 103!

Marking

After classification, packets need to be marked with their appropriate IP precedence or DSCP value. The following is the required configuration for Class Based Marking on CE router.

Marking of Business, Streaming and Voice classes is actually configured through the MQCLI police command, because these classess need to be policed to the SLA limits.

Standard traffic class is not policed, hence we can mark all the traffic with MQCLI “set ip dscp” command.

!policy-map customer_profile class business police 128000 8000 16000 conform-action set-dscp-transmit 10 exceed-action drop class streaming police 64000 2000 2000 conform-action set-dscp-transmit 26 exceed-action drop class voice police 64000 2000 2000 conform-action set-dscp-transmit 46 exceed-action drop class management police 24000 8000 16000 conform-action transmit exceed-action drop class class-default set ip dscp 0!

The following is the required configuration for LPR marking of the locally generated management traffic. As discussed before, ACL 103 matches all management traffic.

!ip local policy route-map management!route-map management permit 10 match ip address 103 ! here we simulate the set ip dscp 48 command set ip precedence 6 set ip tos 0!

In/Out-Contract Traffic Profile

The In/Out-contract design is less restrictive than simple policing of class bandwidth to SLA limit, because it allows customer to exceed the subscribed class-BW thresholds when other classes on CE-PE link are underutilised. This is because in CBWFQ queuing strategy, the bandwidth of underutilised traffic classes can be consumed by other classes proportionally with the respective configured class bandwidths.

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However, the design option described in this chapter has not been recommended to ST, because it involves fairly complex implementation, provisioning and monitoring. It introduces complexity not only on access layer, but QoS implementation in the core has to support it as well.

Instead of policing in each of the traffic classes, it is possible to introduce a mechanism of in / out contract for the Business and Streaming traffic classes. The main reasons behind this recommendation are twofold:

In an MPLS / VPN environment, it should be avoided that well behaving customer sites are penalised by ill-behaving customer sites. A well behaving customer site is a site which sends traffic into the network below the Ingress Committed Rate (ICR), and this on a per traffic class basis. An ill behaving site sends traffic into the network above the ICR for a particular traffic class. The problem is that, if a well behaving site and an ill behaving site both send traffic to a third site, congestion might occur on the egress PE to that site. If there is no way of differentiating between the “well behaving” traffic and “ill behaving” traffic, traffic from the well behaving site might be dropped instead of traffic from the ill behaving site. The introduction of an in / out contract traffic marking mechanism at the ingress CE will prevent this.

The introduction of in / out contract traffic profiles will facilitate the capacity planning of the backbone network which is shared among the different MPLS / VPN customers. Indeed, the shared backbone network needs to be engineered and capacity planned only for the in-contract part of the customer traffic. When, in a second phase, QoS mechanisms are deployed in the core backbone network due to possible backbone congestion, it will be possible to differentiate the out-contract traffic from the in-contract traffic and as a result, discard the out-contract traffic earlier.

The following would be the required configuration for Police marking of the Business, Streaming and Voice traffic classes in ST network:

The in-contract Business traffic is marked as AF11 (DSCP 10). The out-contract Business traffic is marked as AF21 (DSCP 18).

The in-contract Streaming traffic is marked as AF31 (DSCP 26). The out-contract Streaming traffic is marked as AF41 (DSCP 34).

The Voice traffic is marked as EF (DSCP 46). The notion of out-contract traffic does not apply to jitter-sensitive Voice class (WRED is not applicable in LLQ).

!policy-map customer_profile class business police 128000 8000 16000 conform-action set-dscp-transmit 10 exceed-action set-dscp-transmit 18 class streaming police 64000 2000 2000 conform-action set-dscp-transmit 26 exceed-action set-dscp-transmit 34 class voice police 64000 2000 2000 conform-action set-dscp-transmit 46 exceed-action drop!

The following figure depict the in/out-contract marking in Businness and Streaming traffic classes. As previously described, any packets beyond subscribed bandwidth of Business class would be re-coloured and subject to more aggressive WRED dropping profile.

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Figure 59 In/Out-contract Marking and Policing (example for Business class)

The following picture shows a another marking/policing alternative with two SLA limits:

if the traffic rate exceeds the SLA Limit, traffic is re-coloured as out-contract and sent to the wire.

then, if the traffic rate exceeeds Drop Limit, packets are uncoditionally dropped.

This design variation can be implemented through 2 cascaded CAR statements. The first CAR statement will mark the in-contract traffic below the first rate threshold. The second CAR statement will mark the out-contract traffic between the first and second rate thresholds and will also drop the traffic above the second rate threshold.

The following is the required configuration for CAR policing (dropping) of Business and Streaming traffic classes above a second rate threshold. In this particular example, the Business in-contract traffic is limited to 128 Kbps, and the Business out-contract traffic is limited to 256 Kbps. The Streaming in-contract traffic is limited to 64 Kbps, and the Streaming out-contract traffic is limited to 96 Kbps.

This can be also implemented using a two-rate policer as described in http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122newft/122t/122t4/ft2rtplc.htm, but this method is still depreciated due to relatively immature 12.2T IOS release.

Please note that Voice traffic is still policed above the first (SLA-limit) threshold.

!interface Serial0/1 bandwidth 512 rate-limit output access-group 100 128000 8000 16000 conform-action set-dscp-transmit 10 exceed-action continue rate-limit output access-group 100 128000 8000 16000 conform-action set-dscp-transmit 18 exceed-action drop rate-limit output access-group 101 64000 2000 2000 conform-action set-dscp-transmit 26 exceed-action continue rate-limit output access-group 101 32000 2000 2000 conform-action set-dscp-transmit 34 exceed-action drop rate-limit output access-group 102 64000 2000 2000 conform-action set-dscp-transmit 46 exceed-action drop encapsulation ppp clockrate 512000!

SLA Limit

Re-coloringout-contract

Coloringin-contract

x I P payload

18 I P payload

10 I P payload

Marking (MQCLI )Congestion

Management(WRED)

Out-contract traffic droppedbefore any in-contract packet

I P Packet

http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122newft/122t/122t4/ft2rtplc.htm

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Figure 60 CAR based In/Out-contract Marking and Policing

Policing

Policing in Voice traffic class is configured to provide rudimentary call admission thereby policing voice traffic levels into the core network. The Policing is carried out by the exceed-action option on the end of the police command. Anything over the expected number of voice calls bandwidth will not be forwarded. If a customer attempts to exceed this limit then all the calls flowing through that specific CE-PE connection could be affected to degradation in the quality of all the simultaneous calls. However, this affect is much better than single customer affecting all the other customers in ST network sharing a specific backbone link.

The Business and Streaming traffic classes will also be policed to subscribed SLA limits using MQCLI police commands. A few important points surrounding the policing implementation should be understood.

Policing propagates bursts to a certain extent. It does not shape the traffic flow and as such does not cause any packet delay.

Police bandwidths need to be configured in 8 Kbps multiples. This needs to be reflected in the ST service offerings.

Compared to CAR, police bandwidths include some layer-2 overhead (please see the Class Queuing chapter for details).

The police configuration requires the setting of the <normal-burst> NB and <excess-burst> EB parameters. These are parameters used in police’s Token Bucket algorithm.

For TCP oriented classes such as Business class, the recommended settings for rate limit normal and excess burst are:

NB = max(8000, {RTT x Committed Rate in Bytes})

EB = 2 x NB

where RTT is ~ 0.05s

The calculation result is rounded to the nearest 1000-byte boundary. The following table identifies the recommended NB and EB values in function of the access link speed.

Drop

SLA Limit

Drop Limit

Re-coloringout-contract

Coloringin-contractx I P payload

18 I P payload

10 I P payload

Marking (CAR)Congestion

Management(WRED)

Out-contract traffic droppedbefore any in-contract packet

I P Packet

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Table 15 NB and EB settings

Link BW [kbps] NB [byte] EB [byte]

64 8000 16000

128 8000 16000

256 8000 16000

512 8000 16000

1024 8000 16000

2048 12800 25600

34368 214800 429600

100000 625000 1250000

155520 972000 1944000

The recommended settings for rate limit normal and excess burst for the VoIP oriented classes such as Voice class are:

NB = 2000

EB = NB (CBR like policer to avoid jitter)

The following is policing configuration example on 512 kbps link. Please note that configured police limits shall match the definition of class bandwidths in each of traffic classes.

!!policy-map customer_profile class business police 128000 8000 16000 conform-action set-dscp-transmit 10 exceed-action drop class streaming police 64000 2000 2000 conform-action set-dscp-transmit 26 exceed-action drop class voice police 64000 2000 2000 conform-action set-dscp-transmit 46 exceed-action drop class management police 24000 8000 16000 conform-action transmit exceed-action drop class class-default ! Standard class is not policed set ip dscp 0!interface Serial0/1 description CE-PE link bandwidth 512 encapsulation ppp max-reserved-bandwidth 95 service-policy output customer_profile clockrate 512000!

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Class Queuing

Queuing within the classes is implemented through Low latency Queuing (LLQ). LLQ is in fact the combination of Class Based Weighted Fair Queuing (CBWFQ) and Priority Queuing (PQ). The PQ is used for delay sensitive traffic such as VoIP. LLQ is configured through the MQCLI.

Different traffic classes – a maximum of 64 traffic classes can be defined on a single router – can be combined in a service policy. This is kind of a traffic profile. Each of the classes in the service policy will be assigned a minimum bandwidth according to the service contract that has been agreed with the customer. The minimum bandwidth that can be configured is 8 Kbps25. Under congestion, each of the traffic classes will have this minimum bandwidth available:

If one class is congested (and so experiences delay), the congestion is isolated from other classes, which still have a guaranteed minimum share of the link bandwidth.

If one class is under-utilised, other classes can use the available bandwidth26. All flows and classes get a proportionate share of the spare bandwidth. The proportion is dictated by the configured bandwidth for classes where the higher the allocated bandwidth, the higher the proportion allocated. For flow-based weighted fair queuing, configurable in the default-queue, the proportion of available bandwidth is allocated based on the precedence of the packets where the packets with the highest precedence values get the highest proportion of bandwidth.

This enables worst-case bounds on delay and jitter to be designed independently between the classes whilst preventing any single class from being starved by over utilisation on other classes. Also, other parameters like congestion avoidance and control parameters can be configured on a per-class basis. This will be discussed further on.

The sum of the minimum bandwidths reserved for the customer traffic classes needs to be lower than the total link bandwidth. Some bandwidth needs to be reserved for management traffic and routing traffic. Since ST will offer a managed service, it needs to keep control over the CEs, even under congestion circumstances. Also the routing traffic – which is BGP or RIP in this case – needs to have some minimum bandwidth available (8 Kbps or 1 %, whatever is larger).

It should also be understood that the actual minimum bandwidths configured through MQCLI include the following layer 2 overhead, in contrast with CAR which only includes pure layer 3 IP bandwidth. Overhead added by the hardware (CRC, flags) is not included in the MQCLI bandwidths27.

The 8 bytes of SNAP/LLC overhead and 4 bytes of the 8-byte AAL5 trailer for ATM interfaces (the remaining 4 bytes of the AAL5 trailer CRC are not taken into account). AAL5 padding is equally not taken into account. The ATM cell overhead (5 bytes per cell payload of 48 bytes) is not taken into account.

The 4-byte Frame Relay overhead for Cisco Frame Relay encapsulation (additional overhead due to possible FRF.12 headers is not taken into account). CRC and flags overhead is not taken into account.

The 2 bytes of PPP encapsulation overhead.

Also, all reports will indicate the configured rates – so including the L2 overhead. It is worth considering for ST to include the L2 overhead in traffic contracts with customers. This would ensure consistency in between the contracted bandwidths and the performance reports.

After defining the service policy in a policy-map, it needs to be applied on an interface (service-policy).

25 On 10k series the granularity is 1/255th of link bw.26 Except on 10k and 12000 series where LLQ is policed to configured class-bw.27 Except on 10k series, where MQCLI on ATM interfaces inlcudes all layer-2 overhead.

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By default, on the non-distributed router platforms (non VIP based), the sum of the minimum bandwidths needs to be lower than 75 % of the configured access bandwidth. Since the actual required sum of minimum bandwidths will probably be larger, this default parameter setting can be changed (maximum-reserved-bandwidth) to 100 %. However, it is also a very good design practice not to push the design boundaries to the edge without allowing for any margin of error or unexpected traffic patterns. Therefore, it is still recommended to keep the sum of all minimum bandwidths below 100 %. Keeping the sum of all minimum bandwidths around 95 % will allow for unaccounted traffic such as layer 2 overhead, layer 2 keepalives, LMI (in the case of Frame Relay), etc.

The following is the sample configuration for LLQ class queuing. Class bandwidths can be configured in [kbps] or [%] of (max-res-bw – voice-bw).

On 10000 series routers, the cumulative bandwidth applied on traffic classes must not exceed the 99% of link bandwidth. The bandwidth is configurable in steps of 1/255 of link (or PVC) bandwidth. This rule must be respected when configuring the class bandwidths on the CE router.

!policy-map customer_profile class business bandwidth percent 30 class streaming bandwidth percent 20 class voice priority 64 class management bandwidth percent 5 class class-default bandwidth percent 45!interface Serial0/1 bandwidth 512 encapsulation ppp max-reserved-bandwidth 95 service-policy output customer_profile clockrate 512000!

In the configuration template above, the Voice traffic class has been allocated 64kbs of link capacity. The “priority” command guarantees bandwidth to the priority class and restrains the flow of packets from the priority class: when the link is not congested, the priority class traffic is allowed to exceed its allocated bandwidth. When the device is congested, the priority class traffic above the allocated bandwidth is discarded (but we will police it to contractual Voice class bandwidth).

Business, Streaming, Management and Standard classes will share the remaining max-reserverd-bandwidth as configured. For example, the Streaming traffic class will receive minimum bandwidth of ((512*95%)-64)*20% = 84 kbps in congestion periods.

Congestion avoidance

Congestion avoidance techniques monitor network traffic loads in an effort to anticipate and avoid congestion at common network bottlenecks. Congestion avoidance is achieved through packet dropping. Among the more commonly used congestion avoidance mechanisms is Random Early Detection (RED), which is optimum for high-speed transit networks. Cisco IOS QoS includes an implementation of RED

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that, when configured, controls when the router drops packets. If there is no Weighted Random Early Detection (WRED) configured, the router uses the cruder default packet drop mechanism called tail drop.

WRED combine the capabilities of the RED algorithm with the IP Precedence feature. Within the section on WRED, the following related features are discussed:

Tail Drop. Tail drop is the default congestion avoidance behaviour when WRED is not configured. Tail drop treats all traffic equally and does not differentiate between classes of service within the same queue. Queues fill during periods of congestion. When the output queue is full and tail drop is in effect, packets are dropped until the congestion is eliminated and the queue is no longer full.

Weighted Random Early Detection. WRED avoids the globalisation problems that occur when tail drop is used as the congestion avoidance mechanism on the router. Global synchronisation occurs as waves of congestion crest only to be followed by troughs during which the transmission link is not fully utilised. Global synchronisation of TCP hosts, for example, can occur because packets are dropped all at once. Global synchronisation manifests when multiple TCP hosts reduce their transmission rates in response to packet dropping, then increase their transmission rates once again when the congestion is reduced.

About Random Early Detection

The RED mechanism was proposed by Sally Floyd and Van Jacobson in the early 1990s to address network congestion in a responsive rather than reactive manner. Underlying the RED mechanism is the premise that most traffic runs on data transport implementations that are sensitive to loss and will temporarily slow down when some of their traffic is dropped. TCP, which responds appropriately—even robustly—to traffic drop by slowing down its traffic transmission, effectively allows the traffic-drop behavior of RED to work as a congestion-avoidance signalling mechanism.

TCP constitutes the most heavily used network transport. Given the ubiquitous presence of TCP, RED offers a widespread, effective congestion-avoidance mechanism. The minimum threshold value should be set high enough to maximise the link utilisation. If the minimum threshold is too low, packets may be dropped unnecessarily, and the transmission link will not be fully used.

The difference between the maximum threshold and the minimum threshold should be large enough to avoid global synchronisation of TCP hosts (global synchronisation of TCP hosts can occur as multiple TCP hosts reduce their transmission rates). If the difference between the maximum and minimum thresholds is too small, many packets may be dropped at once, resulting in global synchronisation.

Random drops occur once the average queue length exceeds the minimum thresholds, once the average queue equals the maximum threshold the number of dropped packets equals the maximum drop probability value. When the average queue is greater than the maximum threshold then all packets are dropped.

Weighted random early detection

WRED makes early detection of congestion possible and provides for multiple classes of traffic. It also protects against global synchronisation. For these reasons, WRED is useful on any output interface where congestion is expected to occur.

However, WRED is usually used in the core routers of a network, rather than at the edge of the network. Edge routers assign IP precedence to packets as they enter the network. WRED uses this precedence to determine how to treat different types of traffic.

WRED provides separate thresholds and weights for different IP precedence, allowing ability to provide different qualities of service in regard to packet dropping for different traffic types. Standard traffic may be dropped more frequently than premium traffic during periods of congestion.

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DiffServ compliant WRED

DiffServ Compliant WRED extends WRED to support Differentiated Services (DiffServ) and Assured Forwarding (AF) Per Hop Behavior (PHB). This feature enables customers to implement AF PHB by coloring packets according to differentiated services code point (DSCP) values and then assigning preferential drop probabilities to those packets.

The dscp-based argument enables WRED to use the DSCP value of a packet when it calculates the drop probability for the packet. The prec-based argument enables WRED to use the IP Precedence value of a packet when it calculates the drop probability for the packet. After enabling WRED to use the DSCP value, you can then use the new random-detect dscp command to change the minimum and maximum packet thresholds for that DSCP value.

MPLS compliant WRED

The MPLS Compliant WRED feature enables WRED to use the MPLS EXP value when it calculates the drop probability for a packet. The MPLS value is the 3 bits of the MPLS Experimental bits in the label header.

MPLS based WRED is automatically enabled if the transmitting packet has a MPLS header and uses the same values from the precedence configuration.

WRED operation

WRED is a congestion avoidance and control mechanism whereby packets will be randomly dropped when the average class queue depth reaches a certain minimum threshold (min-threshold). As congestion increases, packets will be randomly dropped (and with a rising drop probability) until a second threshold (max-threshold) where packets will be dropped with a drop probability equal to the mark-probability-denominator. Above max-threshold, packets are tail-dropped.

The following picture depicts the WRED algorithm.

Figure 61 WRED Algorithm

WRED will selectively instruct TCP stacks to back-off by dropping packets. Obviously, WRED has no influence on UDP based applications (besides the fact that their packets will be dropped equally).

Avg. length ofclass queue

1

0

minTH maxTH

DropProbab.

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The average queue depth is calculated using the following formula:

new_average = (old_average * (1-2-e) + (current_queue_depth * 2-e)

The “e” is the “exponential weighting constant”. The larger this constant, the slower the WRED algorithm will react. The smaller this constant, the faster the WRED algorithm will react. The exponential weighting constant can be set on a per-class basis. The min-threshold, max-threshold and mark probability denominator can be set on a per precedence or per DSCP basis.

The mark probability denominator should always be set to 1 (100 % drop probability at max-threshold).

WRED design objective in ST

WRED will be applied on the Business, Streaming and Standard traffic classes.

In order to reduce the packet delay and jitter in the Streaming class, smaller min-threshold and max-threshold values will be used compared to the Business and Standard classes.

In order to reduce the packet loss in the Business class, larger min-threshold and max-threshold values will be used compared to the Streaming class.

Again, it should be stressed that tuning QoS parameters is never a straightforward process and the results are depending on a large number of factors, including the offered traffic load and profile, the ratio of load to available capacity, the behaviour of end-system TCP stacks in the event of packet drops, etc. Therefore, it is strongly recommended to test these settings in a testbed environment using expected customer traffic profiles and to tune them, if required. In addition, after an initial production beta deployment, a performance assessment phase and subsequent tuning of the QoS deployment is a necessity.

Minimum and Maximum Thresholds

Each queue has a required length to serve its purpose of attempting to maintain specific maximum delay values. Depending on the service that will be using a specific queue, one may want to increase or decrease the time that packets are allowed in a queue before WRED starts dropping.

Different queue lengths have been selected for each of the defined classes. Each class serves data with distinct delay, jitter and packet loss sensitivities therefore dictating how long a queue can be before packets can be dropped.

The Business traffic class will be servicing mostly TCP data that is somewhat sensitive to delay but more so to packet loss, hence the medium sized queue. The Streaming traffic class will be serving data such as streaming video based on UDP that is sensitive to delay but less so to packet loss. A short queue allows us to estimate end-to-end delay. The Standard traffic class serves best effort data without a specific maximum end-to-end delay or packet loss requirement. A long queue that starts dropping earlier than other queues but at a lower ration because of a shallower RED curve is therefore ideal.

The values used below are estimate values and must be adjusted once ST has a better understanding of their traffic patterns and quality of service.

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The minimum and maximum WRED threshold values are calculated on the basis of the allocated class bandwidth and not on the link bandwidth. This will yield the most realistic results. The following generic formula is used to derive WRED thresholds based on the maximum allowed delay:

The minimum and maximum queue thresholds for each of the service classes will be calculated as follows:

Business Class – Medium Queue – Max per-hop delay 100ms:

Min-threshold = 0.03 x B

Max-threshold = 0.1 x B

With B representing the class bandwidth in MTU sized packets per second. For ST MPLS network a MTU size of 1500 bytes is assumed. On the core trunks the management traffic will be carried in the Business class. For obvious reasons we have to protect the management traffic from customers’ traffic flows with less aggressive packet drop policy. The following are min and max thresholds for management traffic (DSCP 48) within the Business traffic class:



Streaming Class – Short Queue – Max per-hop delay 50ms:



With B representing the bandwidth in MTU sized packets per second. For ST’s MPLS network a MTU size of 1500 bytes is assumed.

Standard Class – Long Queue – Max per-hop delay 150ms:



With B representing the bandwidth in MTU sized packets per second. For ST MPLS network a MTU size of 1500 bytes is assumed.

For Voice traffic it is necessary to implement tail-drop to minimise and predict delay/jitter under congestion conditions. Therefore, no WRED will be used for the Voice traffic class (except on the GSR). WRED will also not be applied to management class.

The WRED min-threshold and max-threshold (calculated on basis of the class bandwidth) settings are as detailed in the following tables. They represent the values to be used across all platforms except for the GSR ENG-2 line cards. These will be presented in GSR QoS design chapter later on.

If ST wishes to offer a class-bw, which is not included in the following tables, the min/max thresholds can be calculated as per formulas above.

maxTH =classBW [byt/s]

MTU [byt]delay [s] *

B [pkts/ s]

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Table 16 WRED Settings for Business Class.

Link Speedin kbps B

Link BW minTH

Link BW maxTH

Class BW 10% in kbps

Class BW 10% minTH

Class BW 10% maxTH


Class BW 20% minTH

Class BW 20% maxTH


Class BW 25% minTH

Class BW 25% maxTH


Class BW 30% minTH

Class BW 30% maxTH

64 6 3 9

128 11 3 9

256 22 3 9

512 43 3 9

1024 86 3 9

2048 171 6 18

10000 834 26 84 1000 3 9 2000 6 17 2500 7 21 3000 8 26

34684 2891 87 290 3468 9 29 6937 18 58 8671 22 73 10405 27 87

100000 8334 251 834 10000 26 84 20000 51 167 25000 63 209 30000 76 251

155000 12917 388 1292 15500 39 130 31000 78 259 38750 97 323 46500 117 388

622000 51834 1556 5184 62200 156 519 124400 312 1037 155500 389 1296 186600 467 1556

2400000

200000 6000 20000 240000 600 2000 480000 1200 4000 600000 1500 5000 720000 1800 6000

For values smaller than E1, on a class percentage, the calculated value will be less than 3 for the MIN Threshold and 9 for the MAX threshold. Any smaller value will defeat the objectives of WRED, seeing that the router would not allow for much burst and react to aggressively in dropping the packets.

These values are therefore no considered in the calculations.

Table 17 WRED Settings for Streaming Class.

Link Speedin kbps B

Link BW minTH

Link BW maxTH


Class BW 10% minTH

Class BW 10% maxTH


Class BW 20% minTH

Class BW 20% maxTH


Class BW 25% minTH

Class BW 25% maxTH


Class BW 30% minTH

Class BW 30% maxTH

64 6 3 9

128 11 3 9

256 22 3 9

512 43 3 9

1024 86 3 9

2048 171 3 9

10000 834 13 42 1000 3 9 2000 3 9 2500 4 11 3000 4 13

34684 2891 44 145 3468 5 15 6937 9 29 8671 11 37 10405 14 44

100000 8334 126 417 10000 13 42 20000 26 84 25000 32 105 30000 38 126

155000 12917 194 646 15500 20 65 31000 39 130 38750 49 162 46500 59 194

622000 51834 778 2592 62200 78 260 124400 156 519 155500 195 648 186600 234 778

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2400000

200000 3000 10000 240000 300 1000 480000 600 2000 600000 750 2500 720000 900 3000

Table 18 WRED Settings for Standard Class.

Link Speedin kbps B

Link BW minTH

Link BW maxTH


Class BW 10% minTH

Class BW 10% maxTH


Class BW 20% minTH

Class BW 20% maxTH


Class BW 25% minTH

Class BW 25% maxTH


Class BW 30% minTH

Class BW 30% maxTH

64 6 3 9

128 11 3 9

256 22 3 9

512 43 3 9

1024 86 4 13

2048 171 8 26

10000 834 38 126 1000 4 13 2000 8 26 2500 10 32 3000 12 38

34684 2891 131 434 3468 14 44 6937 27 87 8671 33 109 10405 40 131

100000 8334 376 1251 10000 38 126 20000 76 251 25000 94 313 30000 113 376

155000 12917 582 1938 15500 59 194 31000 117 388 38750 146 485 46500 175 582

622000 51834 2333 7776 62200 234 778 124400 467 1556 155500 584 1944 186600 700 2333

2400000 200000 9000 30000 240000 900 3000 480000 1800 6000 600000 2250 7500 720000 2700 9000

Drop Probability

The drop probability at max-threshold for all classes will initially be configured as mark-propability-denominator=1. This means that when the average-queue-length reaches the max-threshold, all packets will be dropped until the average goes below the Max-threshold.

The formulae for this is:

This means that when setting the mpd to 2 for instance, ½ according to the formula above represents that at the “max-threshold” only half or rather 50% of the all the packets are being dropped. This also means that the ratio at which the packets are dropped as the average queue length increases is also lower than if the mpd was set “to 1 for instance, seeing that an mpd of 1 actually means that 1/1 or 100% packets are dropped at “max-threshold.

Why is it important to set mpd to 1 rather than to another value? The answer is predictability. When calculating the other values for WRED, we know that any packet after Max-threshold is tail dropped. Therefore, by setting the mpd to 1, we ensure a more realistic drop ratio throughout the WRED curve. If the value was set to 2 for instance, WRED would only drop a number of packets so to reach a 50% drop ratio by the time the average queue depth reaches the Max-threshold and then, all of a sudden, one packet takes it over the Max-threshold and the packet drops go from 50% to 100%.

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Exp. Weighting Const

WRED calculates an exponentially weighted average queue size, rather than the current queue size, when deciding the packet drop probability. The current average queue length depends on the previous average and on the queue's current actual size. In using an average queue size, RED achieved its goal to not react to momentary burstiness in the network and react only to persistent congestion.

With high values of exponential-weighting-constant, the average queue size closely tracks the old average queue size and more freely accommodates changes in the current queue size, resulting in the ability for RED to accommodate temporary bursts in traffic, smoothing out the peaks and troughs in the current queue size. RED is slow to start dropping packets, but it can continue dropping packets for a time after the actual queue size falls below the minimum threshold.

If exponential-weighting-constant is too high, RED does not react to congestion, as the current queue size becomes insignificant in calculating the average queue size. Packets are transmitted or dropped as if RED were not in effect.

With low values of exponential-weighting-constant, the average queue size closely tracks the current queue size, which enables the average queue size to move rapidly with the changing traffic levels. This means the RED process responds quickly to long queues. When the queue falls below the minimum threshold, the process stops dropping packets.

If exponential-weighting-constant it too low, RED overreacts to temporary traffic bursts and drops traffic unnecessarily. The formula for calculating exponential-weighting-constant (ewc) is as follows:

ewc = 10/B if Line Rate (core)/Committed Rate (edge) <= 34Mbps

ewc = 1/B if Line Rate (core)/Committed Rate (edge) > 34Mbps

,where B is the rate of 1500 byte packets (i.e. CEILING(Rate[kbps] * 1000 / 8 / 1500).

The configured exponential-weighting-constant (x) is applied to the router configuration as a negative power of 2. The relation between ewc and the configured value is:

ewc = 2-x which can be rewritten as:

1/ewc = 2x and the final formula for configured ewc is:

x = ln(1/ewc) / ln(2)

x = ln(B/10) / ln(2) if Line Rate (core)/Committed Rate (edge) <= 34Mbps

x = ln(B) / ln(2) if Line Rate (core)/Committed Rate (edge) > 34Mbps

Note:

The exponential-weighting-constant parameter is calculated based on the Class Bandwidth value and NOT on the link rate. For the GSR12000, however, since it is not possible to configure per class, the exponential-weighting-constant is calculated based on the link rate.

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The ewc for Standard class (class-default) shall be based on link rate.

If the Class Bandwidth Allocation is configured as a percentage value in MQC, this should be converted to a value in Kbps for calculating ewc.

The following table computes the exponential-weighting-constant in function of the link speed (GSR) or class speed (10xxx or smaller).

Table 19 WRED - exponential weighting constant

Link Speedin kbps B

B

or

B/10 X

Class BW 10% in kbps B

B

or

B/10 x


B

or

B/10 x


B

or

B/10 x


B

or

B/10 x

32 3 3 3 3.2 1 1 3 6.4 1 1 3 8 1 1 3 9.6 1 1 3

64 6 6 3 6.4 1 1 3 12.8 2 2 3 16 2 2 3 19.2 2 2 3

128 11 11 3 12.8 2 2 3 25.6 3 3 3 32 3 3 3 38.4 4 4 3

256 22 22 4 25.6 3 3 3 51.2 5 5 3 64 6 6 3 76.8 7 7 3

512 43 43 5 51.2 5 5 3 102.4 9 9 3 128 11 11 3 153.6 13 13 4

1024 86 86 6 102.4 9 9 3 204.8 18 18 4 256 22 22 4 307.2 26 26 5

2048 171 171 7 204.8 18 18 4 409.6 35 35 5 512 43 43 5 614.4 52 52 6

10000 834 834 10 1000 84 84 6 2000 167 167 7 2500 209 209 8 3000 250 250 8

34684 2891 289.1 8 3468.4 290 290 8 6936.8 579 579 9 8671 723 723 9 10405.2 868 868 10

100000 8334 833.4 10 10000 834 834 10 20000 1667 1667 11 25000 2084 2084 11 30000 2500 2500 11

155000

12917 1291.7 1g0

15500 1292 1292 10 31000 2584 2584 11 38750 3230 323 8 46500 3875 387.5 9

622000 51834 5183.4 12 62200 5184 518.4 9 124400 10367 1036.7 10 155500 12959 1295.9 10 186600 15550 1555 11

2400000

200000 20000 14 240000 20000 2000 11 480000 40000 4000 12 600000 50000 5000 12 720000 60000 6000 13

The following is the required WRED configuration template on CE-PE link.

!policy-map customer_profile class voice ! class streaming random-detect dscp-based random-detect exponential-weighting-constant <x> random-detect dscp 26 <minTH> <maxTH> 1 class business random-detect dscp-based random-detect exponential-weighting-constant <x> random-detect dscp 10 <minTH> <maxTH> 1 random-detect dscp 48 <minTH> <maxTH> 1 class management ! class class-default random-detect dscp-based

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random-detect exponential-weighting-constant <x> random-detect dscp 0 <minTH> <maxTH> 1 !

SAA-to-PE QoS mechanisms (applied on the SAA)

The SAA routers will be installed in ST PoPs as CE devices with special purpose: gathering of inter-PoP QoS statistics. For this, the SAA router will generate the Probes and measure the QoS attributes like one-way delay or jitter towards any other ST PoP, for each of the traffic classes.

The SAA routers and links between the SAA and PE will be provisioned by the VPNSC (as this is also accomplished for VPN CE routers). This means that VPNSC will also control the configuration of probes that will simulate the customers’ traffic flows across the MPLS network.

Ideally the SAA would generate the probes marked with the DSCP field that reflects the ST CoS design, so that we could reuse the CE configuration templates. Due to the limitation in current VPNSC version, the SAA can only set the IP precedence bits on traffic probes it generates. This requires additional colouring with appropriate TOS value (using the LPR feature), so that resulting DSCP field (Precedence and TOS bits) complies with ST CoS design.

DSCP-based classification of SAA probes is not possible, as locally sourced packets are not CEF switched. We will use access lists to classify the SAA probes into appropriate traffic class.

There’s no need for policing or WRED of SAA probes as the amount of SAA traffic is under control of ST.

Exact class bandwidth requirement will depend on type, number and frequency of SAA probes, and will be determined during and after staging.

The following QoS configuration template will be applied on SAA routers.

hostname xxxSAA1!class-map match-any business match access-group 150class-map match-any streaming match access-group 152class-map match-all voice match access-group 154class-map match-any management match access-group 155!policy-map SAA_profile class business bandwidth percent 35 class streaming bandwidth percent 20 class voice priority 128 class management bandwidth percent 5 class class-default bandwidth percent 40!

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interface Serial<x> description E1 link towards PE bandwidth 2000 encapsulation ppp max-reserved-bandwidth 95 service-policy output SAA_profile clockrate 2000000!! Marking of locally originated SAA probes!ip local policy route-map Mark_SAA_probes!! Classify the SAA probes based on IP precedence!access-list 150 permit ip any any precedence 1 ! Business access-list 152 permit ip any any precedence 3 ! Streaming access-list 154 permit ip any any precedence 5 ! Voiceaccess-list 155 permit ip any any precedence 6 ! Managementaccess-list 156 permit ip any any precedence 0 ! Standard!route-map Mark_SAA_probes permit 10 match ip address 150 152 set ip tos 4!route-map Mark_SAA_probes permit 20 match ip address 154 set ip tos 12!route-map Mark_SAA_probes permit 30 match ip address 155 156 set ip tos 0!

CE-to-PE QoS mechanisms (applied on the PE) – PPP or HDLC

The QoS mechanisms used on the PE (10k and 7206VXR platforms) are basically a subset of the mechanisms used on the non-distributed CE platforms. The configuration on the PEs is almost identical to the one on the CE. There are some differences and these will be highlighted.

Classification

The traffic can be classified on PE routers by matching the DSCP values, because all traffic has already been properly marked on the CEs when entering the network.

Traffic classification on CE-PE connection is required only for packets received from unmanaged CEs and Internet connections as explained below.

Marking

No customer traffic packet marking would be performed on the PE, since all packets have already been marked appropriately on the ingress CEs.

The management traffic generated locally on the PE will be marked through Local Policy Routing (LPR). The configuration template is the same as on the CE router.

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Policing

Traffic has been already policed on the CE router so there’s no need to police the traffic coming from managed CE routers on the PE.

Unmanaged CEs and Unmanaged Internet CPEs

Unmanaged CE means that ST does not have control over the CE router in customer’s premises, i.e. the customer is managing the CE device.

Service without QoS

The decision is that by default no QoS will be implemented and offered to customers with unmanaged CEs. In other words, traffic received from unmanaged CE router will be treated as best effort within the ST MPLS network and as such assigned to Standard traffic class. This is also true for customers who will not subscribe to ST QoS services (even if the CE is managed by ST).

The following configuration template will classify and mark the traffic from unmanaged CE routers28.

!policy-map unmanaged_CE class class-default set ip dscp 0!interface Serial 2/0/1:0 bandwidth <bw> description Link to unmanaged CE service-policy input unmanaged_CE!

The second example shows how the police command can be used to limit the bandwidth on high-speed circuits to subscribed subrate of kbps.

!policy-map limit_customer_512k class class-default police 512000 12800 25600 conform-action set-dscp-transmit 0 exceed- action drop!interface Serial 2/0/1:0 bandwidth 2000 description Link to unmanaged CE with subrate of 512kb service-policy input limit_customer_512k!

Customer configures QoS on the CE router

ST can in theory co-ordinate a proper CE router QoS configuration to the customer (vie e-mail or phone support), but based on our experiences this is in most cases extremely painful procedure for the service provider. QoS configuration, monitoring and troubleshooting is extremely complex task and may result in service disruption if non-skilled customers adjust the QoS parameters on customer-managed CE routers. It is then not trivial to prove to such customer that the ST core network was operating normally when the customer experienced service outage due to QoS misconfiguration!

28 Also, traffic received from upstream transit providers, peering partners and Internet customers must be marked with DSCP 0, to prevent “precedence-spoofing” attacks.

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The following configuration template shows how to re-enforce the policing of traffic classes for unmanaged CE routers. The policy-map would have to be replicated and tuned for each customer.

On the CE side, the QoS configuration template of managed CE can be reused for unmanaged CE routers.

!! Customer has already classified and marked the IP packets on unmanaged CE! The classification class-map is the same as with managed CE routers (the! same config for all CEs)!class-map match-any voice match ip dscp 46class-map match-any management match ip dscp 48 match access-group 103class-map match-any business match ip dscp 10class-map match-all streaming match ip dscp 26!! ST must police the traffic classes according to SLA ! of that customer – this is customer-specific configuration and can result! in a very long router configuration file.!policy-map CUSTx_police class business police <bps> <normal_burst> <ext_burst> conform-action transmit exceed-action drop class streaming police <bps> <normal_burst> <ext_burst> conform-action transmit exceed-action drop class voice police <bps> <normal_burst> <ext_burst> conform-action transmit exceed-action drop class management police <bps> <normal_burst> <ext_burst> conform-action transmit exceed-action drop class class-default set ip dscp 0!interface Serial 2/0/1:0 bandwidth <bandiwdth> description Link to unmanaged CE of customer X service-policy input CUSTx_police

SAA Routers

Traffic received from SAA router will be handled in the same way as packets received from managed CEs. This implies that the set_qos_group service policy shall be configured on SAA links in the same way as already explained for managed CE connections.

PE-to-P QoS mechanisms (applied on the PE)

Classification

The customer traffic received from the CE and SAA routers has been marked with the DSCP. On MPLS uplinks the DSCP value will be automatically mapped in the MPLS EXP bits as shown in Figure 56.

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The following configuration example depicts the EXP based classification on PE-P uplinks. MPLS frames needs to be classified in order to perform queuing and apply proper WRED drop policy.

!class-map match-any business_management match mpls experimental 1 6class-map match-any streaming match mpls experimental 3class-map match-any voice match mpls experimental 5!

Marking

IP packets will be encapsulated in MPLS frames when leaving the PE router. The DSCP code point value (i.e. the precedence bits) will be automatically mapped into EXP bits of MPLS label. No further configuration is needed.

Class queuing

The parameter setting for the reservable interface bandwidth has been changed from 75% (default) to 97% on 7206VXR PE routers This provides enough space for unaccounted traffic such as layer 2 overhead, layer 2 keepalives, LMI (in the case of Frame Relay), etc..

In the following configuration templates, all MQCLI class bandwidth calculations are based on this value.

On 10000 series routers, the cumulative bandwidth applied on traffic classes must not exceed the 99% of link bandwidth. The bandwidth is configurable in steps of 1/255 of link (or PVC) bandwidth.

Furthermore it is important to notice, that on 10000 series POS interfaces the calculation of the minimum class bandwidth is based on the avilable information bandwidth.

For example, the basic rate of STM-1 POS interfaces is 155.520 Mbps. The avilable information bandwidth is 149.760 Mbps (155.520Mbps – Sonet Overhead).

The avilable information bandwidth can be dispalyed with the following commands:

10K-PE#sh hardware pxf cpu queue pos 1/0/0

VCCI 2: Class ID Length/Max Res Dequeues Drops ~ 0 class-default 291 0/1024 3 295173 0...

10K-PE#sh hardware pxf cpu queue 291ID (queue/packet-queue) : 291/291...Bandwidth Index : 73 (149760 kbps)...

As already mentioned above, on 10000 series the LLQ is policed to configured class-bw. This is done by default when configuring ‘priority <bw value>’ command. Neverthless a warning message will be displayed after entering this command:

10K-PE(config-cmap)#policy-map PE_P_155M10K-PE(config-pmap)# class voice

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10K-PE(config-pmap-c)# priority 37587% This command is an unreleased and unsupported feature

For a period of time, the command will still work as it did in the past (even though the warning is displayed). It will disappear in future releases. Therefore we recommend to use the police command within the high priority class on 10000 routers (like shown below).

The following is an example configuration for the class queuing on PE-to-P trunks. The same queuing template must be applied on primary and backup uplinks.

!policy-map PE_P_155M class voice priority police 36312000 conform-action transmit exceed-action drop violate-action drop class business_management bandwidth 36317 class streaming bandwidth 36317 class class-default bandwidth 36317!


WRED is used for graded packet dropping in each traffic class. The DSCP-based WRED is currently supported on MPLS uplinks.

The following configuration template will be used for congestion management on PE-to-P links. WRED thresholds and ewc are derived in the same way as for the CE-to-PE links.

!policy-map PE-P class qos_group_business_management random-detect dscp-based random-detect exponential-weighting-constant 9 random-detect dscp 10 117 388 1 random-detect dscp 48 388 775 1 class qos_group_streaming random-detect dscp-based random-detect exponential-weighting-constant 8 random-detect dscp 26 49 162 1 class class-default random-detect dscp-based random-detect exponential-weighting-constant 11 random-detect dscp 0 146 485 1 !

PE-P, P-P and P-PE QoS mechanisms (applied on the P)

On new Engine 3 GSR linecards the QoS implementation is slightly different from the currently used linecards. MQCLI will be introduced on GSR. This is described in a separate chapter (see ).

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Class Queuing (MDRR)

MDRR is architecturally different from LLQ where bandwidth is not reserved per class but rather weights or ”timeslots” are allocated for each class. With MDRR we have the ability to manipulate queue weights to define the quantum or time spent servicing a queue. Also, like the PQ in LLQ, MDRR has a low latency queue typically used for servicing real-time traffic such as voice. The low latency queue will shall be set to ”alternate priority”.

The GSR also differs architecturally from the other platforms in that it maintains two instances of queuing with MDRR during the flow of a packet from the input interface to the output interface. The first instance is called “to fabric” and the second instance is called “from fabric”.

“To-fabric” or RX-COS MDRR

The “to-frabric” MDRR is applied exactly as the name implies – packets exiting a line card to the switching fabric. The considerations to take here are that, unlike “from fabric” queuing, one does not know the destination port line speed but still need to take all possibilities into account. Consider the following:

Packets come in from a high speed STM-16 port and are destined to exit through a lower speed STM-1 card. Clearly, this will cause congestion. The ability to push back the congestion management to before the packets hit the switching fabric is clearly beneficial. Therefore, when creating a traffic management policy or “cos-group” as it is known in MDRR, one must first create one for each available interface in the chassis. In ST, the “to-fabric” and “from-fabric” cos-groups are the same because we want the same behaviour at both queuing instances.

The application method is as follows:

For packets destined to a slot with an STM-1 line card, an STM-1 cos-group will be applied, regardless of what the source line card is.

For packets destined to a slot with an STM-16 line card, an STM-1 cos-group is applied if the source line card is STM-16, STM-16 cos-group if the source is an STM-16.

In doing so, one applies the cos-group depending on what the destination slot is, therefore avoiding “congestion” on the switching fabric.

“From-fabric” or TX-COS MDRR

The “from-fabric” MDRR is a lot simpler is terms of configuration. The queueing occurs at the egress to the TX-queue. At this stage, one knows the exit slot and interface speed. The cos-group is simply applied to the actual interface, just like a service policy is applied to an interface on a 7XXX platform.

MDRR queuing operation

Each DRR queue can be given a relative weight, with one of the queues in the group is defined as a low latency queue. This is done via the queue command under the cos-queue-group.

queue <0-6> <1-2048>queue low-latency [alternate-priority | strict-priority] <1-2048>

The weights give a relative bandwidth for each queue when the interface is congested. The DRR algorithm de-queues data from each queue in turn if there is data in the queue to be sent. So if all the regular DRR queues have data in them they will be serviced as the following:

0-1-2-3-4-5-6-0-1-2-3-4-5-6...

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On each time through cycle the queue will get to packet de-queue the quantum Q that is proportional to the configured queue weight W. Packet de-queue quantum Qn is:

Qn = MTU + (Wn - 1)*512

A value of 1 is equivalent of giving the interface a weight of its MTU. For each increment above 1, the weight of the queue increases by 512 bytes. For example, if the MTU of a particular interface is 4470 and the weight of a queue is configured to be 3, each time through the rotation 4470 + (3-1)*512 = 5494 bytes will be allowed to be de-queued. If for example 2 normal DRR queues, Queue0 and Queue1 are used, Queue0 is configured with a weight of 1 and Queue1 configured with a weight of 9. If both queues were congested, each time through the rotation Queue0 would be allowed to send 4470 bytes and Queue1 would be allowed to send 4470 + (9-1)*512 = 8566 bytes. This would give traffic going Queue0 approximately 1/3 of the bandwidth and the traffic going through Queue1 about 2/3.

The low latency queue can be added to give more priority to certain traffic. The low latency queue can be given 2 different priorities within the group. It can be put in strict priority or in alternating priority. In strict priority, this queue is serviced whenever it is non-empty.

To minimize the jitter in Voice class of ST network, the LLQ will be configured in strict priority mode.

The following table gives an example for MDRR weights that can be used on the ST network as initial queuing and class capacity definition. Weights have been calculated following the algorithm above.

MTU on POS links is 4470.

Table 20 MDRR weights

Service Class % of link BW Queue STM-1 STM-16

Class BW [Mbps] Weight Class BW [Mbps] Weight

Voice 20 low latency 31 10 480 10

Business, Mgmt 30 2 48 13 720 13

Streaming 25 1 38 10 600 10

Standard 25 0 38 10 600 10

MDRR configuration guide for ST

From-fabric (TX COS)

Each interface has eight COS queues, which can be configured independently. Flexible mapping between IP precedence and the eight possible queues is offered in the MDRR implementation. MDRR allows a maximum of eight queues so that each IP precedence value can be made its own queue. The mapping is flexible; however, the number of queues needed and the precedence values mapped to those queues are user-configurable. It is possible to map one or more precedence values into a queue.

The ST network will have four queues,

Low-Latency Queue. Low-latency queue will be an alternate priority queue; this will be for VoIP traffic packets marked with MPLS EXP 5 will be forwarded to this queue. 25% of the available physical bandwidth will be available for voice traffic.

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Queue 2 will be used for Business and Management traffic classes. Packets marked MPLS EXP 1 and 6 will be forwarded to this queue. 25% of the available physical bandwidth will be available for Business and management traffic.

Queue 1 will be the Streaming data queue for delay sensitive traffic but variable packet sizes. Packets marked with MPLS EXP 3 will be forwarded to this queue. 25% of available physical bandwidth will be available for streaming traffic.

Queue 0 will be for default-classified traffic – i.e. Standard traffic class. MPLS EXP 0 will be forwarded to this queue. 25% of the available physical bandwidth will be available for best-effort traffic.

The following commands are an example configuration in the ST network. The same MDRR TX-COS configuration could be applied to STM-1 and STM-16 links, but the WRED parameters will be different. So we have to have one cos-queue-group per link capacity. However, the same cos-queue-group can be applied on RX and TX side; this will reduce the size of router configuration file.

The precedence-based configuration acts on EXP bits in the case of MPLS packets.

!cos-queue-group STM<1,16> ! Duplicated for each rate, same for RX and TX side prec 0 queue 0 ! Map the packet with PREC/EXP=0 into queue 0 prec 1 queue 2 prec 2 queue 2 prec 3 queue 1 prec 4 queue 1 prec 5 queue low-latency prec 6 queue 2 prec 7 queue 2 queue 0 10 queue 1 10 queue 2 13 queue low-latency strict-priority 10!interface pos 3/1 description This is STM-1 backbone link tx-cos STM1

To-fabric or RX COS

In addition to the transmit COS, a receive COS will also be configured. The queues will be identical to the interface transmits queues, but instead of being applied directly to the line interface they are built as a table and applied from the receive buffer to the backbone fabric buffers.

With the cards supplied for ST MDRR is supported in hardware, each line card has eight COS queues per destination interface. With 16 destination slots and 16 interfaces per slot, the maximum number of COS queues is 16 X 16 X 8 = 2048. All the interfaces on a destination slot have the same COS parameters.

In the example, the slot-table-cos stm-to-fabric command defines the COS policy for destination line cards 2,3 and 5,6 based on the STM-1 and STM-16 cos-queue-group. The rx-cost-slot command applies the stm-to-fabric slot-table-cos configuration to a particular slot (line card). As previously mentioned, the cos-groups will be applied as follows:

For packets destined to a slot with an STM-1 line card, an STM-1 cos-group will be applied, regardless of what the source line card is.

For packets destined to a slot with an STM-16 line card, an STM-1 cos-group is applied if the source line card is STM-1, STM-16 cos-group if the source is an STM-16.

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!rx-cos-slot 2 STM1-TO-FABRIC ! We have STM-1 interfaces in this slotrx-cos-slot 3 STM1-TO-FABRIC ! We have STM-1 interfaces in this slotrx-cos-slot 5 STM16-TO-FABRIC ! We have STM-16 interfaces in this slotrx-cos-slot 6 STM16-TO-FABRIC ! We have STM-16 interfaces in this slot!slot-table-cos STM1-TO-FABRIC destination-slot all STM1!slot-table-cos STM16-TO-FABRIC destination-slot 2 STM1 destination-slot 3 STM1 destination-slot 5 STM16 destination-slot 6 STM16!

Congestion management

WRED parameters on GSR routers will follow the guidelines already explained for CE and PE routers. The GSR-specific configuration is depicted in this chapter.

Exponential weighting constant

On GSR the ewc cannot be configured on a per-class basis. For this reason, the link bandwidth will be used to calculate the ewc. According to Table 19 the ewc for STM-1 links will be 10, and for STM-16 links the ewc will have the value of 14.

Policing of Voice class with WRED

Because the provisioning rule for ST is max. 20% Voice traffic on a link, congestion in the Voice class would therefore be highly unlikely and if at all, only under extreme cases such as multiple flows from STM-16 links to a single STM-1. Nonetheless the remote possibility of this occurring should be prevented.

In the GSR and MDRR, tail-drop or control of the LLQ is not possible. In order to achieve this, a WRED setting will be applied on the LLQ. The MIN/MAX-threshold settings will be calculated based on a maximum delay of 3ms and an average packet size of 64 bytes. The idea is to allow a small burst. The MIN-threshold will therefore be quite small and the MAX-threshold will be equal to the MIN.

Random-detect-label 5 will be used to apply WRED on the Voice traffic (valid for ENG-2 linceards as well).

Max-threshold (Voice) ~ 0.003 x B [256 for STM-1, 2048 for STM-16]

Min-threshold = Max-threshold

where B = bandwidth in MTU sized packets. For Voice an MTU of 64 bytes is assumed.

WRED on Engine-2 Linecards

The following three tables represent the WRED Min and Max settings for the ENG-2 linecards on the GSR platforms. The reason that slightly different values have been allocated is due to architectural design. The constraint being that the difference between the minTH and maxTH values must be a power of 2.

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The basis for the calculation is still the same with the same base values being used to calculate the minTH and initial maxTH. Once the two threshold values have been worked out, the difference between the two is derived (Delta1). If the value of the difference between the Min and Max threshold is not a power of 2 then a new value is assigned (Delta2) and added to the original minTH to derive a new and valid maxTH. When linecard assigns Delta2 as a difference, the closest value to the original difference (Delta1) is used. The following example demonstrates this:

Min Threshold = 39

Max Threshold = 130

Difference (Delta1) = 91

Assigned Difference (Delta2) is either 64 or 128

New Assigned Difference = 64 (closer to 91 than 128)

New Max Threshold = 103

Table 21 WRED Setings for Business Class (ENG-2 GSR)

Table 22 WRED Setings for Streaming Class (ENG-2 GSR)

Table 23 WRED Setings for Standard Class (ENG-2 GSR)

WRED Configuration

This is an example configuration template for WRED on STM-1 GSR links. In case of ENG-2 linecards the thresholds need to be adjusted as described above.

Please note that “precedence x random-detect-label y” statements apply to IP packets with precedence x and also to MPLS frames with EXP bits set to x. “y” here refers to index of WRED profile.

!cos-queue-group STM1 ! Duplicated for each STM rate with precedence 0 random-detect-label 0 ! appropriate WRED thresholds and EWC precedence 1 random-detect-label 1 precedence 2 random-detect-label 0 precedence 3 random-detect-label 3 precedence 4 random-detect-label 0 precedence 5 random-detect-label 5

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precedence 6 random-detect-label 6 precedence 7 random-detect-label 6 random-detect-label 0 146 485 1 ! Standard random-detect-label 1 117 388 1 ! Business random-detect-label 3 49 162 1 ! Streaming random-detect-label 5 180 181 1 ! Voice (3ms tail-drop of 64byt packets) random-detect-label 6 388 775 1 ! Routing & Management exponential-weighting-constant 10 ! 10 is default!

PE to CE QoS mechanisms (applied on the PE)

Classification

The traffic will be classified by matching the DSCP values, for scheduling onto PE-CE connection. Management traffic is carried in a dedicated Management class on PE-CE links. Classification of locally sourced traffic with LPR has already been demonstrated.

The following configuration template will classify the traffic for queuing and congestion management on PE-CE link (outbound direction).

!class-map match-any business match ip dscp 10class-map match-any streaming match ip dscp 26class-map match-any voice match ip dscp 46class-map match-any management match ip dscp 48!

Class queuing

The following is the sample configuration for the class queuing on PE-to-CE links. Please note that class bandwidths shall match with those configured on the CE side.

!policy-map PE-CE class business bandwidth percent 35 class streaming bandwidth percent 20 class voice priority 64class management bandwidth percent 5 class class-default bandwidth percent 40!interface Serial 2/0/1:1.1 description PE-CE access layer link bandwidth 512 encapsulation ppp max-reserved-bandwidth 95 service-policy output PE-CE!

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WRED one PE-CE link shall be configured with the same parameters as on the CE router. Below is a sample configuration template.

!policy-map PE-CE class voice ! class streaming random-detect dscp-based random-detect exponential-weighting-constant <x> random-detect dscp 26 <minTH> <maxTH> 1 class business random-detect dscp-based random-detect exponential-weighting-constant <x> random-detect dscp 10 <minTH> <maxTH> 1 class management! class class-default random-detect dscp-based random-detect exponential-weighting-constant <x> random-detect dscp 0 <minTH> <maxTH> 1 !

QoS mechanisms on ATM PVCs (applied on the CE and PE)

ATM PVCs can be used in between the CE and PE. This section describes the design modification required on the ATM CEs and PEs. It is assumed that both the CE and PE make use of the ATM port adapter which supports IP to ATM CoS. This means basically that we can do LLQ on a per ATM VC basis. This section only highlights the differences in comparison with the previous configurations. Please refer to the relevant sections on CE and PE QoS configurations for a complete overview.

It is important to understand that ATM introduces a significant amount of overhead, which is not always accounted for in the QoS configuration bandwidths. This overhead needs to be taken into account when performing capacity planning and when provisioning the network. The following is a short summary of the ATM overhead that can be incurred.

SDH STM-1 used on the PE has 90 bytes of overhead in each 2430-byte OC-3c frame. This means 3.70 % is not available for higher-level protocols. This overhead is not taken into account in the LLQ bandwidths.

PDH E3 used on the CE uses G.804 / G.832 framing to map ATM cells into the payload of an E3 circuit. Each frame is 537 bytes which includes 7 bytes of overhead. This 1.30% overhead is not available for higher level protocols. This overhead is not taken into account in the LLQ bandwidths.

ATM cells are 53 bytes long containing a 5 byte header and a 48 byte payload. This adds 9.43% overhead that is not available for higher level protocols. This overhead is not taken into account in the LLQ bandwidths.

The AAL5 protocol overhead consists of a trailer at the end of the AAL5 PDU. This trailer occupies the last 8 bytes of the last cell of the PDU. In addition AAL5 specifies that a cell may only belong to a single PDU so any payload available in the ATM cell after the AAL5 trailer has been added as the last 8 bytes of the cell, cannot be used. With an IP MTU of 576 bytes this adds a 6.41% overhead. This overhead in only partly taken into account in the LLQ bandwidths (the AAL5 trailer, but without 4 bytes of the CRC and without any padding).

RFC 1483 LLC encapsulation requires LLC, OUI and Ethertype headers to precede the IP datagram. This overhead amounts to 8 bytes per datagram. With an IP MTU of 576 bytes this adds a 1.37% overhead. This overhead is taken into account in the LLQ bandwidths.

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Operation, Administration and Maintenance (OAM) cell overhead. This overhead is not taken into account in the LLQ bandwidths.

Assuming an IP MTU of 576 bytes (Internet inter-network default) then each layer contributes the following percentage overhead to transmit an IP datagram.

Table 24 ATM Overhead

WAN Link Protocol Layer % Overhead

ATM STM-1 SDH STM-1 3.70

ATM 9.43

AAL5 6.41

LLC / SNAP 1.37

Total 20.91

ATM E3 PDH E3 1.30

ATM 9.43

AAL5 6.41

LLC / SNAP 1.37

Total 18.51

The following table summarises which overhead is or is not included in the MQCLI LLQ bandwidth statements.

Table 25 LLQ bandwidths and ATM

Overhead Length Included in MQCLI

RFC 1483 LLC / SNAP header 8 bytes Yes

AAL5 trailer 8 bytes Partially. 4-byte CRC field is not included

AAL5 padding to make last cell an even multiple of 48 bytes Variable No

ATM cell header 5 bytes No

Due to the significant ATM overhead that is not accounted for in the MQCLI bandwidths, it is recommended to allocate not more than 80 % (a conservative figure) of the total available ATM bandwidth to LLQ traffic classes. The ATM PVC bandwidth for a VBR-nrt ATM CoS is defined as the Sustained Cell Rate (SCR). In other words, not more than 80 % of a particular PVC SCR should be allocated in service policies attached to that PVC.

On the PE and CE routers (except on 75xx), the amount of bandwidth that can be applied to interfaces in service policies can be controlled through the “max-reserved-bandwidth” bandwidth command. The default is 75 %.

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The following is the required configuration for applying the service policy to an ATM PVC. ATM traffic shaping needs to be configured on the ATM PVC. ATM traffic shaping is a mechanism that alters the traffic characteristics of a stream of cells on a connection to achieve better network efficiency by ensuring conformance at a policed remote ATM switch interface. Traffic shaping must maintain cell sequence integrity on a connection.

!interface ATM5/1 no ip address max-reserved-bandwidth 80!interface ATM5/1.50 point-to-point

ip address n.n.n.n n.n.n.n pvc 50/105 vbr-nrt <SCR> <PCR> <MBS> service-policy output customer_profile!

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High Availability

This chapter would dicuss the high availability comppnent as it relates to the propose architecture. Depending on the size of the content this chapter and next may be combined

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Security

This chapter would dicuss the high availability comppnent as it relates to the propose architecture. Depending on the size of the content this chapter and next may be combined. Some very general topics are presented here as a sample

Password Management

Passwords and similar secrets (such as SNMP community strings) are the primary defence against unauthorized access to your router. The best way to handle most passwords is to maintain them on a TACACS+ or RADIUS authentication server. However, almost every router will still have a locally configured password for privileged access, and may also have other password information in its configuration file.

The enable secret command is used to set the password that grants privileged administrative access to the IOS system. An enable secret password should always be set. You should use enable secret, not the older enable password because the later uses a weak encryption algorithm.

If no enable secret is set, and a password is configured for the console TTY line, the console password may be used to get privileged access, even from a remote VTY session. This is almost certainly not what you want, and is another reason to be certain to configure an enable secret.

The service password-encryption command directs the IOS software to encrypt the passwords, CHAP secrets, and similar data that are saved in its configuration file. This is useful for preventing casual observers from reading passwords, for example, when they happen to look at the screen over an administrator's shoulder.

However, the algorithm used by service password-encryption is a simple Vigenere cipher; any competent amateur cryptographer could easily reverse it in at most a few hours. The algorithm was not designed to protect configuration files against serious analysis by even slightly sophisticated attackers, and should not be used for this purpose. Any Cisco configuration file that contains encrypted passwords should be treated with the same care used for a clear text list of those same passwords.

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This weak encryption warning does not apply to passwords set with the enable secret command, but it does apply to passwords set with enable password.

The enable secret command uses MD5 for password hashing. The algorithm has had considerable public review, and is not reversible as far as anybody at Cisco knows. It is, however, subject to dictionary attacks (a "dictionary attack" is having a computer try every word in a dictionary or other list of candidate passwords). It's therefore wise to keep your configuration file out of the hands of untrusted people, especially if you're not sure your passwords are well chosen.

Console Ports

It is important to remember that the console port of an IOS device has special privileges. In particular, if a BREAK signal is sent to the console port during the first few seconds after a reboot, the password recovery procedure can easily be used to take control of the system. This means that attackers who can interrupt power or induce a system crash, and who have access to the console port via a hardwired terminal, a modem, a terminal server, or some other network device, can take control of the system, even if they do not have physical access to it or the ability to log in to it normally.

It follows that any modem or network device that gives access to the Cisco console port must itself be secured to a standard comparable to the security used for privileged access to the router. At a bare minimum, any console modem should be of a type that can require the dialup user to supply a password for access, and the modem password should be carefully managed.

Controlling TTY’s

Local asynchronous terminals are less common than they once were, but they still exist in some installations. Unless the terminals are physically secured, and usually even if they are, the router should be configured to require users on local asynchronous terminals to log in before using the system. Most TTY ports in modern routers are either connected to external modems, or are implemented by integrated modems; securing these ports is obviously even more important than securing local terminal ports.

By default, a remote user can establish a connection to a TTY line over the network; this is known as "reverse Telnet," and allows the remote user to interact with the terminal or modem connected to the TTY line. It is possible to apply password protection for such connections. Often, it is desirable to allow users to make connections to modem lines, so that they can make outgoing calls. However, this feature may allow a remote user to connect to a local asynchronous terminal port, or even to a dial-in modem port, and simulate the router's login prompt to steal passwords, or to do other things that may trick local users or interfere with their work.

To disable this reverse Telnet feature, apply the configuration command transport input none to any asynchronous or modem line that should not be receiving connections from network users. If at all possible, do not use the same modems for both dial-in and dial-out, and do not allow reverse Telnet connections to the lines you use for dial-in.

Controlling VTYs and Ensuring VTY Availability

Any VTY should be configured to accept connections only with the protocols actually needed. This is done with the transport input command. For example, a VTY that was expected to receive only Telnet sessions would be configured with transport input telnet, while a VTY permitting both Telnet and SSH sessions would have transport input telnet ssh. If your software supports an encrypted access protocol such as SSH, it may be wise to enable only that protocol, and to disable clear

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text Telnet. It's also usually a good idea to use the ip access-class command to restrict the IP addresses from which the VTY will accept connections.

A Cisco IOS device has a limited number of VTY lines (usually five). No additional remote interactive connections can be established if all of the VTY’s are in use. This creates the opportunity for a denial-of-service attack; if an attacker can open remote sessions to all the VTY’s on the system, the legitimate administrator may not be able to log in. The attacker does not have to log in to do this; the sessions can simply be left at the login prompt.

One way of reducing this exposure is to configure a more restrictive ip access-class command on the last VTY in the system than on the other VTY’s. The last VTY (usually VTY 4) might be restricted to accept connections only from a single, specific administrative workstation, whereas the other VTY’s might accept connections from any address in a corporate network.

Another useful tactic is to configure VTY timeouts using the exec-timeout command. This prevents an idle session from consuming a VTY indefinitely. Although its effectiveness against deliberate attacks is relatively limited, it also provides some protection against sessions accidentally left idle. Similarly, enabling TCP keepalives on incoming connections (with service tcp-keepalives-in) can help to guard against both malicious attacks and "orphaned" sessions caused by remote system crashes.

Disabling all non-IP-based remote access protocols, and using IPSec encryption for all remote interactive connections to the router can provide complete VTY protection. IPSec is an extra-cost option, and its configuration is beyond the scope of this document.

Logging

Cisco routers can record information about a variety of events, many of which have security significance. Logs can be invaluable in characterizing and responding to security incidents. The main types of logging used by Cisco routers are:

AAA logging, which collects information about user dial-in connections, logins, logouts, HTTP accesses, privilege level changes, commands executed, and similar events. AAA log entries are sent to authentication servers using the TACACS or RADIUS protocols, and are recorded locally by those servers, typically in disk files. If you are using a TACACS or RADIUS server, you may wish to enable AAA logging of various sorts; this is done using AAA configuration commands such as aaa accounting.

SNMP trap logging, which sends notifications of significant changes in system status to SNMP management stations.

System logging, which records a large variety of events, depending on the system configuration. System logging events may be reported to a variety of destinations, including the following:

o System console port (logging console).

o Servers using the syslog protocol (logging <ip-address>, logging trap).

o Sessions on VTY’s and TTY’s (logging monitor, terminal monitor).

o Local buffer in router RAM (logging buffered).

Console logging shall be disabled during debugging of various router protocols to prevent router “freeze”

From a security point of view, the most important events usually recorded by system logging are interface status changes, changes to the system configuration, access list matches, and events detected by the optional firewall and intrusion detection features.

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Each system-logging event is tagged with an urgency level. The levels range from debugging information (at the lowest urgency), to major system emergencies. Each logging destination may be configured with threshold urgency, and will receive logging events only at or above that threshold.

Saving logging information

By default, system-logging information is sent only to the asynchronous console port. Since many console ports are unmonitored, or are connected to terminals without historical memory and with relatively small displays, this information may not be available when it is needed, especially when a problem is being debugged over the network.

Almost every router should save system logging information to a local RAM buffer. The logging buffer is of a fixed size, and retains only the newest information. The contents of the buffer are lost whenever the router is reloaded. Even so, even a moderately sized logging buffer is often of great value. On low-end routers, a reasonable buffer size might be 16384 or 32768 bytes; on high-end routers with lots of memory (and many logged events), even 262144 bytes might be appropriate. You can use the show memory command to make sure that your router has enough free memory to support a logging buffer. Create the buffer using the logging buffered <buffer-size> configuration command.

Larger installations will have syslog servers. You can send logging information to a server with logging <server-ip-address>, and you can control the urgency threshold for logging to the server with logging trap <urgency>. Even if you have a syslog server, you should still enable local logging.

If your router has a real-time clock or is running NTP, you will probably want to time-stamp log entries using service timestamps log|debug datetime msecs.

Recording Access List Violations

If you use access lists to filter traffic, you may want to log packets that violate your filtering criteria. Older Cisco IOS software versions support logging using the log keyword, which causes logging of the IP addresses and port numbers associated with packets matching an access list entry. Newer versions provide the log-input keyword, which adds information about the interface from which the packet was received, and the MAC address of the host that sent it.

It is not usually a good idea to configure logging for access list entries that will match very large numbers of packets. Doing so will cause log files to grow excessively large, and may cut into system performance. However, access list log messages are rate-limited, so the impact is not catastrophic.

Access list logging can also be used to characterize traffic associated with network attacks, by logging the suspect traffic.

Anti-spoofing

Many network attacks rely on an attacker falsifying, or spoofing the source addresses of IP datagrams. Some attacks rely on spoofing to work at all, and other attacks are much harder to trace if the attacker can use somebody else’s address. Therefore, it is valuable for network administrators to prevent spoofing wherever feasible.

Anti spoofing should be done at every point in the network where it is practical, but is usually both easiest and most effective at the borders between large address blocks, or between domains of network

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administration. It is usually impractical to do anti-spoofing on every router in a network; because of the difficulty of determining which source addresses may legitimately appear on any given interface.

For an Internet service provider effective anti-spoofing, together with other effective security measures, can cause expensive, annoying problem subscribers to take their business to other providers. ISP’s should be especially careful to apply anti-spoofing controls at dialup pools and other end-user connection points (see also RFC 2267).

Administrators of firewalls or perimeter routers sometimes install anti-spoofing measures to prevent hosts on the Internet from assuming the addresses of internal hosts, but do not take steps to prevent internal hosts from assuming the addresses of hosts on the Internet. It's a far better idea to try to prevent spoofing in both directions. There are at least three good reasons for doing anti-spoofing in both directions at an organizational firewall:

Internal users will be less tempted to try launching network attacks and less likely to succeed if they do try.

Wrongly configured internal hosts will be less likely to cause trouble for remote sites.

Outside crackers often break into networks as launching pads for further attacks. These crackers may be less interested in a network with outgoing spoofing protection.

Anti-spoofing with packet filters

Unfortunately, it is not practical to give a simple list of commands that will provide appropriate spoofing protection; access list configuration depends too much on the individual network. However, the basic goal is simple: to discard packets that arrive on interfaces that are not viable paths from the supposed source addresses of those packets. For example, on a two-interface router connecting a corporate network to the Internet, any datagram that arrives on the Internet interface, but whose source address field claims that it came from a machine on the corporate network, should be discarded.

Similarly, any datagram arriving on the interface connected to the corporate network, but whose source address field claims that it came from a machine outside the corporate network, should be discarded. If CPU resources allow it, anti-spoofing should be applied on any interface where it is feasible to determine what traffic may legitimately arrive.

ISPs carrying transit traffic have limited opportunities to configure anti-spoofing access lists, but can usually at least filter outside traffic that claims to originate within the ISP's own address space.

In general, anti-spoofing filters must be built with input access lists; that is, packets must be filtered at the interfaces through which they arrive at the router, not at the interfaces through which they leave the router. This is configured with the ip access-group <list> in interface configuration command. It is possible to do anti-spoofing using output access lists in some two-port configurations, but input lists are usually easier to understand even in those cases. Furthermore, an input list protects the router itself from spoofing attacks, whereas an output list protects only devices behind the router.

Please note that anti-spoofing filters can increase operational/management complexity. Some large VPNs may change or update their address allocation on a daily or weekly basis, which means that ST operations will have to maintain and update packet-spoofing filters accordingly. The fact that IP packets from a given VPN can’t escape into any other VPN somehow eliminates the need for use of anti-spoofing filters. A misbehaved customer can only attack its own sites. A MPLS/VPN customer cannot affect any other MPLS/VPN customer, nor the ST backbone routers.

Inbound anti spoofing filter are implemented on IPv4 (Internet) connections:

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IPv4 CPE-PE interfaces on the PE routers.

Peering interfaces on iGWs.

Virtual-template and other dialup interfaces.

Access interfaces on IPv4 CE routers.

Access list 101 consists of the following major sections:

Block packets with invalid or prohibited source IP address from being sent towards or across ST backbone

Improve protection of P and RR routers by only allowing PING and TRACEROUTE traffic to hit the IP address block 213.81.248.0/20 (ie. the address block reserved for Backbone links).

Allow any other packet that is not destined (ie. transit traffic) towards ST backbone

Controlling Directed Broadcasts

IP directed broadcasts are used in the extremely common and popular “smurf” denial-of-service attack, and can also be used in related attacks.

An IP directed broadcast is a datagram which is sent to the broadcast address of a subnet to which the sending machine is not directly attached. The directed broadcast is routed through the network as a unicast packet until it arrives at the target subnet, where it is converted into a link-layer broadcast. Because of the nature of the IP addressing architecture, only the last router in the chain, the one that is connected directly to the target subnet, can conclusively identify a directed broadcast. Directed broadcasts are occasionally used for legitimate purposes, but such use is not common outside the financial services industry.

In a smurf attack, the attacker sends ICMP echo requests from a falsified source address to a directed broadcast address, causing all the hosts on the target subnet to send replies to the falsified source. By sending a continuous stream of such requests, the attacker can create a much larger stream of replies, which can completely inundate the host whose address is being falsified.

If a Cisco interface is configured with the no ip directed-broadcast command, directed broadcasts that would otherwise be expanded into link-layer broadcasts at that interface are dropped instead. The command no ip directed-broadcast must be configured on every interface of every router that might be connected to a target subnet; it is not sufficient to configure only firewall routers. The no ip directed-broadcast command is the default in Cisco IOS software version 12.0 and later. In earlier versions, the command should be applied to every LAN interface that is not known to forward legitimate directed broadcasts.

IP Source Routing

The IP protocol supports source routing options that allow the sender of an IP datagram to control the route that datagram will take toward its ultimate destination, and generally the route that any reply will take. These options are rarely used for legitimate purposes in real networks. Some older IP implementations do not process source-routed packets properly, and it may be possible to crash machines running these implementations by sending them datagrams with source routing options.

A Cisco router with no ip source-route set will never forward an IP packet, which carries a source routing option. You should use this command unless you know that your network needs source routing.

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It is strongly recommended to disable the IP source routing option in ST MPLS network.

ICMP Redirects

An ICMP redirect message instructs an end node to use a specific router as its path to a particular destination. In a properly functioning IP network, a router will send redirects only to hosts on its own local subnets, no end node will ever send a redirect, and no redirect will ever be traversed more than one network hop. However, an attacker may violate these rules; some attacks are based on this. It is a good idea to filter out incoming ICMP redirects at the input interfaces of any router that lies at a border between administrative domains, and it is not unreasonable for any access list that is applied on the input side of a Cisco router interface to filter out all ICMP redirects. This will cause no operational impact in a correctly configured network.

Note that this filtering prevents only redirect attacks launched by remote attackers. It's still possible for attackers to cause significant trouble using redirects if their host is directly connected to the same segment as a host that's under attack.

CDP

Cisco Discovery Protocol (CDP) is used for some network management functions, but is dangerous in that it allows any system on a directly connected segment to learn that the router is a Cisco device, and to determine the model number and the Cisco IOS software version being run. This information may in turn be used to design attacks against the router. CDP information is accessible only to directly connected systems. The CDP protocol may be disabled with the global configuration command no cdp running. CDP may be disabled on a particular interface with no cdp enable.

NTP

The Network Time Protocol (NTP) is a protocol used to time-synchronize network devices. NTP runs over UDP and is documented in RFC 1305. An NTP stratum 1 server should get its time from an authoritative time source, such as a GPS system or an atomic clock attached to a timeserver. NTP then distributes this time across the network. NTP is a very sophisticated and efficient protocol, which only needs one packet per minute to synchronize two machines to within a millisecond of one another.

NTP uses the concept of a "stratum" to describe how many NTP "hops" away a machine is from an authoritative time source. A "stratum 1" time source has a reference clock such as a GPS or atomic clock directly attached, a "stratum 2" time source receives its time from a "stratum 1" time source, and so on. This “hop” count isn’t related to the IP hops between two NTP time sources. A device running NTP automatically chooses the lowest stratum timeserver as its time source. It only talks and listens to servers, which it has a configuration entry for.

To avoid synchronization problems NTP has two methods to determine the validity of the time source. NTP will never synchronize to a device, which is not synchronized itself. It will also not synchronize to a source; whichs time is significantly different than all the other time sources.

The NTP configuration is usually static. Every device has a list of IP addresses with which it will exchange NTP messages. These communication agreements are called associations. On LAN segments NTP can use IP broadcast messages as well.

With Cisco two mechanisms are available to secure the communication: an access list-based restriction scheme and an encrypted authentication mechanism. A limitation of Cisco’s implementation is that it

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doesn’t support stratum 1 service, which means a reference clock such as a GPS or atomic clock cannot be connected directly to the Cisco box.

NTP is a very valuable tool for reporting and troubleshooting, because cause and effect of problems can be clearly correlated. Care must be taken, where the time information comes from, especially if additional time sources from the Internet are used as a reference. Confusing the time system can render system log files completely useless.

The Network Time Protocol (NTP) will be used to synchronize router clocks. NTP authentication will used to have secure NTP associations. The loopback0 address is used to form NTP associations.

ntp authentication-key 1 md5 *&^^&*_(_ 7ntp authenticatentp trusted-key 1ntp source Loopback0ntp update-calendarntp server <P1 loopback> key 1ntp server <P2 loopback> key 1

P1 and P2 shall synchronise with an external timeserver. P1 and P2 routers synchronise among themselves as NTP peers to increase the stability. Any other device in ST network becomes a NTP client of P1 and P2.

ntp peer <P1 loopback>ntp server <ST public NTP server> ntp master 5ntp update-calendar

The PE routers synchronise with the P routers.

ntp server <Primary P>ntp server <Backup P>

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Network Management

Depending on the size of the content there is a possibility that there would be a separate LLD on Network Management. In that case put a reference to that doc. Otherwise discuss in detail all the aspects of Network Management here

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Appendix I

Appendix II

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