© 2006 cisco systems, inc. all rights reserved.cisco public 1 implementing enterprise wan links...
TRANSCRIPT
© 2006 Cisco Systems, Inc. All rights reserved. Cisco Public 1
Implementing Enterprise WAN Links
Introducing Routing and Switching in the Enterprise – Chapter 7
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Objectives
Describe the features and benefits of common WAN connectivity options.
Compare and configure common WAN encapsulations.
Describe Frame Relay
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7.1 WAN Devices and Technology WAN Services purchased
Serial transmissions verses Ethernet in LANS
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7.1 WAN Devices and Technology
Translation device – prepare data for transmission: modem (analog) or CSU/DSU (digital)
Central Office (CO) and Customer Premises Equipment (CPE)
Demarc - point at which responsibility of the customer ends and the service provider begins
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7.1 WAN Devices and Technology Local loop – last mile (first mile for customer)
CSU/DSU or modem – controls the rate data moves onto the loop (DCE), also provides clocking signal to router (DTE)
Various physical layer protocols used
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7.1 WAN Devices and Technology
Note: DS0 – Digital Signal 0, T1 (DS1) = 24 DS0s
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Activity 7.1.1.5
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Activity 7.1.1.5
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7.1.2 WAN Standards
Layer 2 WAN protocols:
LAPF
HDLC
PPP
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7.1.2 WAN Standards
Activity 7.1.2.2
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7.1.2 WAN Standards
Activity 7.1.2.2
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7.1.3 Accessing the WAN
Modems enable POTS to be used for WAN connections
Modems are also used for DSL and cable connections to ISP
A modem encodes the information onto that carrier wave before transmission and then decodes it at the receiving end
The modulated carrier wave carries information to destination across the telephone network
Destination demodulates the carrier and extracts information
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7.1.3 Accessing the WAN DSO channel = time slice of the physical bandwidth
Fractional connections – part of a T1
Two techniques which information from multiple channels can be allocated bandwidth on a single cable based on time:
Time Division Multiplexing (TDM) - if a sender has nothing to say, its time slice goes unused, wasting valuable bandwidth.
Statistical-Time Division Multiplexing (STDM) - dynamically reassigns unused time slices on an as-needed basis, minimizes wasted bandwidth
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Activity 7.1.3.4
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Activity 7.1.3.4
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7.1.4 Packet and Circuit Switching
Dedicated Leased Line – point-to-point serial
Circuit switching: Dedicated bandwidth
Higher cost
Higher level of security
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7.1.4 Packet and Circuit Switching
Packet switching:Bandwidth efficiency
Identifier on each packet
Preconfigured, but non-exclusive, link
Cell switching: high-speed packet switching
ATM (fixed length cells)
Large amount of overhead
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7.1.4 Packet and Circuit Switching
Virtual circuitsSwitched virtual circuits - dynamically established between two points when a router requests a transmission
Permanent virtual circuits - provides a permanent path to forward data between two points (Frame Relay)
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7.1.5 Last mile and long range WAN technologies
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7.1.5 Last mile and long range WAN technologies
Elements of Layer 2 encapsulationsFlag
Address
Control
Protocol
Data
FCS
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7.1.5 Last mile and long range WAN technologies
Great Distances with FiberSynchronous Optical Network (SONET)
Synchronous Digital Hierarchy (SDH)
SDH and SONET are used for moving both voice and data.
New developments for extremely long - dense wavelength division multiplexing (DWDM) - can carry IP, SONET, and ATM data concurrently
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Activity 7.1.5.3
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Activity 7.1.5.3
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7.2.1 Ethernet and WAN Encapsulations
Encapsulation occurs before data travels across the WAN
Layer 2 adds header information specific to the type of physical network transmission
LAN – Ethernet
WAN – depends on link
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7.2.2 Comparing Common WAN Encapsulations
Data Link Layer encapsulation may change continuously to match the technology in use
Network Layer encapsulation will not change
Packets exit the LAN by way of the default gateway router
Router strips off the Ethernet frame and then re-encapsulates that data into the correct frame type for the WAN - acts as a media converter, by adapting the Data Link Layer frame format to a format that is appropriate to the interface
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7.2.2 Comparing Common WAN Encapsulations
Standard bit-oriented Layer 2 encapsulation: HDLC
Cisco HDLC: additional Type fieldDefault WAN encapsulation on Cisco devices
Allows multiple Network Layer protocols to share a link
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7.2.2 HDLC and PPP
Point-to-Point Protocol (PPP):
Data Link Layer encapsulation for serial links
Uses a layered architecture to encapsulate & carry multi-protocol datagrams over a point-to-point link
Standards-based
Support Asynchronous serial
Synchronous serial
Support High-Speed Serial Interface (HSSI)
Integrated Services Digital Network (ISDN)
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7.2.2 HDLC and PPP
PPP has two sub-protocols:Link Control Protocol - responsible for establishing, maintaining and terminating the point-to-point link.
Network Control Protocol - provides interaction with different Network layer protocols.
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7.2.2 HDLC and PPP
Link Control Protocol negotiates: Authentication – PAP and CHAP
compression
error detection
multilink
PPP callback
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7.2.2 HDLC and PPP
Phases of PPP sessions:Link-establishment - Receipt of the configuration acknowledgement frame completes this phase
Authentication (optional) - provides password protection to identify connecting routers
NCP negotiation - The show interfaces command reveals the LCP and NCP states.
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Activity 7.2.2.5
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Activity 7.2.2.5
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7.2.3 Configuring PPP
Change encapsulation from HDLC to PPP on both ends of link
Configure desired optional featuresppp multilink
Configures load balancing across multiple links.
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7.2.3 Configuring PPP
Verification and troubleshooting commands:
show interfaces serial - Displays the encapsulation and the states of the Link Control Protocol (LCP).
show controllers - Indicates the state of the interface channels and whether a cable is attached to the interface
debug serial interface - Verifies the incrementation of keepalive packets.
debug ppp - Provides information about the various stages of the PPP process, including negotiation and authentication
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7.2.3.3 Configuring PPP
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7.2.4 PPP Authentication
Occurs after establishment of the link but before the Network Layer protocol configuration
Password Authentication Protocol (PAP)PAP sends the username/password pair across the link repeatedly in clear text
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7.2.4 PPP Authentication
Challenge Authentication Protocol (CHAP)uses a three-way handshake. 1.PPP establishes the link phase.
2.Local router sends a challenge message to the remote router.
3. Remote router uses the challenge and a shared secret password to generate a one-way hash.
4. Remote router sends back one-way hash to the local router.
5. Local router checks the response against its own calculation, using the challenge and the same shared secret.
6. Local router acknowledges authentication if values match.
7. Local router immediately terminates connection if the values do not match.
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7.2.4 PPP Authentication
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7.2.4 PPP Authentication
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7.2.5.3 LAB – Configuring PAP and CHAP
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Describe Frame Relay Nonbroadcast multiaccess network
Packet switching with variable length packets
STDM
Virtual circuit between two DTE devices
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Describe Frame Relay
Data link connection identifier (DLCI)
Inverse ARP
LMI
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Describe Frame Relay
Service parameters:
Committed information rate (CIR)
Excess information rate (EIR)
Discard eligible (DE) frames
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Describe Frame Relay
Traffic management:
Forward explicit congestion notification (FECN)
Backward explicit congestion notification (BECN)
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Summary Circuit switching WAN technologies create a physical
circuit between end devices before sending data
Packet and cell switching WAN technologies use virtual circuits to send data across the network
Layer 2 encapsulation changes as frames move across a WAN
PPP permits many advanced features including authentication, compression, and load balancing
Frame Relay is a packet switched technology using switched or permanent virtual circuits
Frame Relay uses parameters such as CIR to establish the bandwidth used on each VC
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