Bridge ProtocolsIEEE 802.1 Spanning Tree Learning Bridge

Protocol (STP) IEEE Standard 802.1 is a bridging protocol STP defines forwarding table operation for bridges that

span multiple networks It provides the function of frame (packet) forwarding

table It is dynamic and corrects forwarding problems such as

forwarding loops or unavailable circuit paths. Each data frame passing through a bridge is examined

and forwarded on through a process called filtering

IEEE 802.1 Spanning Tree Learning Bridge Protocol (STP) (Continue…)

STP is a true bridging protocol and is inefficient and disadvantageous when used as a large networking protocol.

STP is better utilized when the network is made up of many point-to-point circuits.

STP elimination of loop paths ties up expensive leased-line resources.

Spanning tree table building after network failures takes considerable time and introduces long user delays.

IBM Source Routing Protocol (SRP) The IBM SRP allows LAN workstations to specify their

routing for each packet transmitted Each packet transmitted by a workstation on the LAN to

the bridge contains a complete set of routing information for the bridge to route upon

The information for source routing to perform its function is contained in the routing information field within the MAC sublayer frame

Refer to Figure 8.1 (p. 281) IBM’s Token Ring implementation of source routing has

a seven-hop count maximum

Source Route Transparent (SRT) Bridging IEEE SRT marries the IEEE STP and the SRP into one bit-

selective bridging protocol Many bridges achieve forwarding rates of over 14,500

frames per second sustained over a long period of time using this technique.

SRP has more overhead than SRT, but the processing is reduced for each bridge it traverses

SRT can also allow SNA source routing into Ethernet TCP/IP networks and DECnet networks

Source Routing Extensions Many vendors such as Bay Networks and Cisco Systems

have implemented extensions to the SRB protocol. These routers, while providing bridging capability, can

transit bridged traffic across an entire WAN composed of multiple routers, and still the entire network will only count as a single hop (eliminating the seven-hop count restriction)

Routing tables are built dynamically through use of the source route explorer packets

This method improves reliability of transmission, eliminates the hop count restriction, and can decreases response time across the network.

Routing Protocols Routers perform both routing and bridging functions.

However, both methods require that the router performs address translation.

There are multiple routing protocols that build forwarding tables using different metrics

Routers use a series of algorithms to perform the task of routing, along with dynamic routing tables to manage this routing

Almost all routers support bridging protocols, as it is preferable to perform translation bridging with a router as opposed to encapsulation bridging with a bridge

Routing Protocols Defined Routing, or gateway protocols, provide router-to-router

communications between like routers using routing tables.

Communications can take place between autonomous systems and within autonomous systems

EGP, IGRP, RIP, BGP, OSFP, IS-IS Serial line protocols provide communications over serial

or dial-up links between unlike routers

HDLC, PPP, SLIP Gateway protocols pass the routing table information and

“keep alive” packets, and the serial line protocol passes the true user data

Routing Protocols Defined (Continue…) Routers need to determine the best way to reach an

address through a network of nodes. Routing algorithms generally exchange information

about a topology based upon in one or two generic methods Distance vector: algorithms use neighbor nodes to

periodically exchange vectors of the distance to every destination in the network

Link state: algorithms have each router learn the entire link state topology of the entire network. This is currently done by flooding only changes to the link state topology through the network

Routing Protocols Defined (Continue…) The link state approach is more complex, but converges

much more rapidly Convergence is the rate at which a network goes from

an unstable state to a stable state

Distance Vector Routing Protocols It is used by the Internet’s Routing Information Protocol (RIP). A key advantage of the distance vector is its simplicity A key disadvantage is that the topology information message

grows larger with the network and the time for it to propagate through the network increases as the network grows IP RIP automatically summarizes at the edges of a class

(A,B,C) network OSFP can be configured to summarize on more arbitrary

area boundaries IPX RIP doesn’t do any summarization at all

Refer to Figure 8.2 (p. 284)

Distance Vector Routing Protocols (Continue…)

RIP Operates in a connectionless mode at the application

layer, interfacing with transport layer protocols through UDP

Its decision for routing is based upon hop count only (no length of the hop)

This can cause problems when a higher-bandwidth path is available and desirable for transport

Refer to Figure 8.3 (p. 285) RIP has a hop-count restriction of 16 hops, and is

prone to routing loops if misconfigured

Distance Vector Routing Protocols (Continue…) IGRP

Superior than RIP because it understands bandwidth limitations between hops, as well as time delays

It is tunable to make it faster if desired It doubles the transmit time of information between

nodes, amplifying the opportunity for a convergence problem

EGP and BGP Exterior routing protocols used between separately

administered networks ISPs use BGP to share routing information between their

networks

Link State Routing Protocols The link state advertisement method was designed to

address the scalability issues of the distance vector method. Routing tables are exchanged with neighbors, but every

device on the network must be at least one other device’s neighbor

Link state updates are sent using 64-byte packets (depending on the specific protocol) in a multicast mode, and require acknowledgments

This protocol will also notify users if their address is unreachable

This method is more memory intensive for the router, and requires large amounts of buffers and memory space

Link State Routing Protocols (Continue..) There are three major implementations of link state

routing protocols on the market: Open Shortest Path First (OSPF):

Based upon shortest path, bandwidth available, cost in dollars, congestion, interface costs, and time delay

All costs for links are designated on the outbound router port

Supports point-to-point, broadcast, and NonBroadcast MultiAccess (NBMA).

OSFP is only useful with TCP/IP networks

Link State Routing Protocols (Continue..) Intermediate System to Intermediate System (IS-IS)

Used to route between network nodesAn extension of IS-IS (Dual IS-IS) can support both

OSI and TCP/IP networks simultaneouslyHowever, OSPF provides a wider range of interface

costs than IS-IS Novell’s NLSP

Proprietary Novell protocol Refer to Table 8.1 (p. 297)

Network and Transport Layer Protocols- The Internet Protocol Suite (TCP/IP)

Structure of TCP/IP TCP provides a reliable, sequenced delivery fo data to

applications. UDP only provides an unacknowledged datagram

capability TCP also provides adaptive flow control, segmentation,

and reassembly, and prioritized data flows. Refer to Figure 8.4 (p. 289) A number of applications interface to TCP and UDP: FTP,

TELNET, SNMP, TFTP, RPC, NFS

IP Packet Formats Refer to Figure 8.5 (p. 290)

Internet Protocol (IP) Addressing Uses 32-bit IP addresses as a global addressing scheme IP addresses are grouped into classes A, B, C Refer to Figure 8.6 (p. 291) Internet addresses are assigned and managed by Internet

Assigned Numbers Authority (IANA) IP works with TCP for end-to-end reliable transmission of

data across the network TCP will control the amount of unacknowledged data in

transit by reducing either the window size or the segment size

TCP/IP Functions IP provides a connectionless datagram delivery service

to the transport layer TCP provides an end-to-end reliable delivery, error

control, retransmission, or flow control Refer to Figure 8.7 (p. 292) IP provides the means for devices to discover the

topology of the network, as well as to detect changes of state in nodes, links, and hosts

Refer to Figure 8.8 (p 294)

Traffic and Congestion Control Aspects of TCP/IP

TCP flow control uses a sliding window flow-control protocol, like X.25

However, the window is of a variable size, instead of the fixed window size used by X.25

Refer to Figure 8.9 (p. 294)

Service Aspects of TCP/IP TCP/IP implementations typically constitute a router, TCP/IP

workstation and server software, and network management. Operation of IP over a number of network, data link, and

physical layer services is defined.

IP Next Generation (IPng)-IPv6 Expands the address size from 32 to 128 bits Simple dynamic auto-configuration capability Easier multicast routing with addition of “scope” field Anycast feature-send packet to anycast address and it is delivered

to one of the nodes which allows nodal routing control Capability to define quality of service to a traffic flow added Reduction of overhead-some header fields are optional More flexible protocol design for future enhancements Authentication, data integrity, and confidentiality options Easy transition and interoperability with IPv4 Support for all IPv4 routing algorithms (e.g., OSPF, RIP, etc)

Legacy SNA SNA still maintains the predominant corporate

mainframe architecture, accounting for over 50 percent of world-wide data communications networks.

Traditional SNA architecture is master-slave and thus hierarchical in nature.

SNA is now moving toward a more distributed, peer-to-peer architecture called Advanced Peer-to-Peer Networking (APPN)

Building Blocks of Traditional SNA Host Processor: is also called a Central Processing Unit

(CPU). Devices include the IBM 3090, 4381, and 9370

Cluster Controller or Terminal Controllers: control a cluster of 8 to 32 typically coax-attached terminals and printers.

Refer to Figure 8.11 (p. 298) Refer to Figure 8.12 (p. 298) Establishment Controller Units: or ECUs are a form of

cluster controllers that can act as a gateway for mainframe connectivity to a Token Ring or Ethernet LAN for VTAM access.

Refer to Figure 8.13 (p. 299)

Communications Controllers (CCs) or Front-End Processors (FEPs): provide access for connecting cluster controllers to a mainframe through a Network Control Protocol (NCP).

FEPs perform front-end processing for the host, route data within the SAN protocol stack between CCs, and can act as concentrators to multiple controllers, terminals, and other communication devices.

Refer to Figure 8.14 (p. 300) Refer to Figure 8.14 (p. 301) Refer to Figure 8.15 (p. 301)

Interconnect Controllers: such as the IBM 3172 provide direct connection for a mainframe to an Ethernet, Token Ring, or FDDI LAN user access to VTAM

Refer to Figure 8.17 (p. 302) IBM Minicomputers: such as the AS400 and System/36

form the cornerstone of most APPN networks. Communications Access Methods: include both

ACF/VTAM and ACF/TCAM Operating Systems (OS) include MVS/XA, MVS/ESA,

DOS/VSE, and OS/2 Host Applications: include CICS,IMS/DC, and TSO

Network Addressable Units - PUs, LUs, and Domains

Synchronization of communications, resource management, and control of the network are managed by Network Addressable Units (NAUs) LU (logical unit) - are “sessions” between end-user access ports

on the network PU (physical unit) - manages the LU SSCP (systems services control point) - defines a single point

for domain control

A network device PU, LU, SSCP is combined to form the network addressable unit (NAU), which forms the network address for a given device.

Network Addressable Units - PUs, LUs, and Domains (Continue…)

Each device in the network is labeled a node An area controlled by one host is called the domain The primary communications protocol is SDLC Refer to Figure 8.18 (p. 304)

SNA Legacy Software Communications Virtual Telecommunications Access Method (VTAM) is the

software that resides in the host computer and communicates with the “dumb” terminals attached to the 3174

The FEP runs a software called Network Control Program (NCP)

IBM SNA/SDLC Migration to LAN/WAN Internetworking

One of the advantages of placing SNA traffic over a WAN is that broadcast packets and unnecessary polling overhead can be eliminated, similar to a more dynamic method of filtering

There are many methods of tying SNA networks into the non-SNA WAN environment

SNA over X.25 - NPSI IBM offers software and hardware called the Network

Control Protocol (NCP) Packet Switching Interface (NPSI) as one option for encapsulating SDLC traffic for transport across the WAN

NPSI encapsulates SNA traffic into X.25 packets Refer to Figure 8.19 (p. 305)

QLLC Conversion - SNA over X.25 The requirement for NPSI can be eliminated by

attaching a Token Ring interface to the 3475, and translating from MAC to QLLC protocol

Refer to Figure 8.20 (p. 305)

PAD/FRAD SDLC/Bisync/Async Consolidation/Encapsulation

Automatic teller machines (ATMs) use the bisync protocol to communicate their transactions back to the controller.

Low-speed SNA traffic using Async (polled and nonpolled), Bisync, and SDLC can be aggregated into a single device and the protocol encapsulated into a single protocol for access to the WAN.

Refer to Figure 8.21 (p. 307)

Traditional Source Route Bridging (SRB) and Remote SRB (RSRB)

SNA traffic can be bridged between Toekn Ring LANs and across the WAN

Replacing point-to-point SDLC links with a Token Ring connection eliminates polling across the entire WAN

Refer to Figure 8.22 (p. 308) While SRB offers a simplistic approach, it has many

problems associated with it

SDLC to LLC2 Protocol Conversion To methods to consolidate IBM 3x74 devices into a

single FEP SDLC to LLC2 protocol conversion Serial tunneling solution

In SDLC to LLC2 conversion, remote 3x74 devices can connect via SDLC to a TCP/IP router. The router will then convert the SDLC traffic into Token Ring format LLC2

LLC2 encapsulation is performed at logical link layer 2 Refer to Figure 8.23 (p. 309) An external device other than the WAN router is

sometimes used to convert the SNA SDLC to LLC2

SNA SDLC Serial tunneling (Synchronous Pass-Through over IP)

One method of routing point-to-point 3270 traffic from an IBM 3174 cluster controller is through SDLC serial tunneling, also called synchronous pass-through

The router encapsulates the SDLC traffic into an IP packet and routes it through the network

Synchronous or transparent pass-through, or tunneling, provides point-to-point mapping with IP encapsulation of the SNA SDLC traffic

Refer to Figure 8.24 (p. 310)

Remote SDLC/3270 polling with retransmission

Eliminates polling overhead with a technique called spoofing or local acknowknowledge

The access device passes only blocks containing SNA data over the dedicated SNA line. Polling is done locally with both primary and secondary modules performing the polling functions.

Refer to Figure 8.25 (p. 311) Two variations

encapsulation (or packetization) of SNA traffic or emulation

routing of PU2s and PU4s in native mode

Remote SNA switching with host pass-through This replaces the primary and secondary polling nodes with

primary and secondary SNA nodes in the router This provides dynamic path routing rather than the SNA-

specified routing, and eliminates the need to establish SNA cross-domain host sessions

Refer to Figure 8.26 (p. 311)

SNA Routing Method 1: APPN Type 4 routing establishes an optimum

path between routers for host communications through router emulation of SNA type 4 routing

Method 2: SNA cross domain type 5/4 host/FEP routing

RFC 1434, DLSw (RFC 1795), DLSw+, and RSRB

DSLw was developed to allow basic transport of SDLC traffic routed within TCP/IP

DLSw+ was designed to fix the scalability problems of DLSw by counting the entire TCP/IP network as a single “hop”, regardless of how many devices the network uses.

Refer to Figure 8.28 (p. 313)

RFC 1490 - SNA and Multiprotocol Traffic Encapsulation across FR Networks

TCP/IP encapsulation over FR offers the ability to perform routing and nondisruptive rerouting

of SNA traffic Refer to Figure 8.29 (p. 315)

Remote bridging over FR Routers located at every site perform a triple encapsulation of

the SNA data within LLC, MAC, and then FR frames Refer to Figure 8.30 (p. 315)

Native LLC2 over FR Use of native LLC2 over FR for direct FEP connection Refer to Figure 8.31 (p. 315)

Advanced Program-to-Program Communication (APPC)

provides peer-to-peer intelligent sessions between peripheral PU2.1 nodes

This constitutes an LU6.2 device-to-LU6.2 device session without involving the host using VTAM and the front-end processor using NCP

APPC supports both dynamic and automatic routing between LU6.2 devices, but it does not support multiple protocols nor mainframe to terminal traffic

The main limitations to APPC are the huge amount of memory (up to 500K) required to run a workstation and the lack of software support.

Advanced Peer-to-Peer Networking (APPN) It allows routing LAN traffic independent of a front-end

processor or a mainframe between workstations or peer devices called End Nodes (ENs).

ENs are typically LU workstations running APPN software The routing devices between ENs, such as FRADs and

routers, are called Network Nodes (NNs). Refer to Figure 8.32 (p. 318) APPN moves users away from FEPs and mainframes and

toward routers Unfortunately, the entire network-routed topology is stored

at each node, and error check and recovery with retransmission of lost packets is performed at each node in the network

Channel Extension - Cisco’s Channel Interface Processor (CIP)

Cisco has available a method of providing a VTAM-to-TCP/IP gateway that uses the direct interface from the host to the router via the older bus-and-tag interface or the newer 17 Mbps ESCON channel interface

Since TCP/IP and VTAM run in the mainframe, no 3172 and no NCP are required.

Refer to Figure 8.33 (p. 319)

NETBIOS/NETBEUI NETBIOS is predominantly used as the PC LAN program

networks and transport protocol in Token Ring implementations.

The IBM NETBIOS Extended User Interface (NETBEUI) allows NETBIOS to be transparently passed over the 802.2 LLC protocol and interface accessing the token ring adapter at the MAC layer

SNA-to-OSI Gateway Implementing a full SNA-to-OSI gateway is an

expensive alternative

CiscoCisco

IP Routing

Objectives

Understand the IP routing processCreate and verify static routingCreate and verify default routingResolve network loops in distance-

vector routingConfigure and verify RIP routingConfigure and verify IGRP routing

Routing

Definition

What must routers know?

IP Routing Process

IP Routing Process (cont.)

IP Routing Process (cont.)

IP Routing in a Larger Network

2621A Configuration

Router>enRouter#config tRouter(config)#hostname 2621A2621A(config)#interface fa0/02621A(config-if)#ip address

172.16.10.1 255.255.255.02621A(config-if)#no shut

2501A Configuration

Router>enRouter#config tRouter(config)#hostname

2501A2501A(config)#int e02501A(config-if)#ip

address 172.16.10.2 255.255.255.0

2501A(config-if)#no shut2501A(config-if)#s02501A(config-if)#ip

address 172.16.20.1 255.255.255.0

2501A(config-if)#no shut

2501B ConfigurationRouter>enRouter#config tRouter(config)#hostname 2501B2501B(config)#int e02501B(config-if)#ip address

172.16.30.1 255.255.255.02501B(config-if)#no shut2501B(config-if)#s02501B(config-if)#ip address

172.16.20.2 255.255.255.02501B(config-if)#clock rate 640002501B(config-if)#no shut2501B(config-if)#int s12501B(config-if)#ip address

172.16.40.1 255.255.255.02501B(config-if)#clock rate 640002501B(config-if)#no shut

2501C Configuration

Router>enRouter#config tRouter(config)#hostname 2501C2501C(config)#int e02501B(config-if)#ip address

172.16.50.1 255.255.255.02501C(config-if)#no shut2501C(config-if)#s02501C(config-if)#ip address

172.16.40.2 255.255.255.02501C(config-if)#no shut

IP Routing in Our Network

Routing tables Configuration Types of routing

StaticDefaultDynamic

Static Routing

DefinitionBenefitsDisadvantagesAdding a static route:ip route [destination_network] [mask] [next_hop_address or exitinterface]

[administrative_distance] [permanent]

2621A & 2501A

Router>enRouter#config tRouter(config)#hostname 2621A2621A(config)#interface fa0/02621A(config-if)#ip address

172.16.10.1 255.255.255.02621A(config-if)#no shut2621A(config-if)#exit2621A(config)#ip route 172.16.20.1

255.255.255.0 172.16.10.22621A(config)#ip route 172.16.30.0

255.255.255.0 172.16.10.22621A(config)#ip route 172.16.40.0

255.255.255.0 172.16.10.22621A(config)#ip route 172.16.50.0

255.255.255.0 172.16.10.2

--------2501A(config)#ip route

172.16.30.0 255.255.255.0 172.16.20.2

2501A(config)#ip route 172.16.40.0 255.255.255.0 172.16.20.2

2501A(config)#ip route 172.16.50.0 255.255.255.0 172.16.20.2

2501B & 2501C

2501B(config)#ip route 172.16.10.0 255.255.255.0 172.16.20.1

2501B(config)#ip route 172.16.50.0 255.255.255.0 172.16.40.2

2501C(config)#ip route 172.16.10.0 255.255.255.0 172.16.40.1

2501C(config)#ip route 172.16.20.0 255.255.255.0 172.16.40.1

2501C(config)#ip route 172.16.30.0 255.255.255.0 172.16.40.1

Default Routing

Definition

Configuration

Default Routing Configuration

2501C(config)#no ip route 172.16.10.0 255.255.255.0 172.16.40.1

2501C(config)#no ip route 172.16.20.0 255.255.255.0 172.16.40.1

2501C(config)#no ip route 172.16.30.0 255.255.255.0 172.16.40.1

2501C(config)#ip route 0.0.0.0 0.0.0.0 172.16.40.1

2501C(config)#ip classless

Dynamic Routing

Definition

Types of Routing Protocols Interior Gateway Protocol (IGP) Exterior Gateway Protocol (EGP)

Administrative Distances

Classes of Routing Protocols

Classes

Distance Vector

Link State

Hybrid

Distance-Vector Routing Protocols

Distance-Vector Routing Start-up

Routing Loops

Stopping Routing Loops

Maximum Hop Count

Split Horizon

Route Poisoning

Holddowns

Routing Information Protocol (RIP)

A true distance-vector protocol Sends updates every 30 seconds on all

active interfaces Only uses hop count

Maximum allowable hop count of 15

Good for small networks Inefficient on large networks or slow

WAN links

RIP

RIP Timers Route update timer Route invalid timer Route flush timer

Configuring RIP Routing2621A(config)#router rip2621A(config)#network

172.16.0.02621A(config)#^Z2621A#

RIP (cont.)

Verifying the RIP Routing Tables2621A(config)#sh ip route

Holding Down RIP PropagationRouterA#config t

RouterA(config)#router ripRouterA(config-router)#network 10.0.0.0RouterA(config-router)#passive-interface

serial 0

Interior Gateway Routing Protocol (IGRP)

DefinitionIGRP Timers

Update timers Invalid timers Holddown timers Flush timers

Configuring IGRP RoutingRouterA(config)#router igrp 10RouterA(config-router)#network 172.16.0.0

Verifying IGRP

Routing Tables2621A#sh ip route

Configurationsshow ip routeshow protocolsshow ip protocoldebug ip ripdebug ip igrp eventsdebug ip igrp transactions

Summary

Stated the IP routing processCreated and verified static routingCreated and verified default routingResolved network loops in distance-

vector routingConfigured and verified RIP routingConfigured and verified IGRP routing