Cisco 思科 网络 技术 培训 技术CHAP17

Cisco 思科 网络 技术 培训 文档

Objectives Upon completion of this chapter, you will be able : to Understand Frame Relay terminology Describe the components and terminology used in Frame Relay networks Compare different topology options available in Frame Relay designs, recognizing the costs and the benefits of each

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Cisco 思科 网络 技术 培训 文档

Chapter Topics Frame Relay overview Advantages Access devices Services Switching operation/LMI

Router interaction RFC 1490 DLCI mapping/Inverse ARP

Network types NBMA Subinterfaces

Topology options

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Cost and Latency of Point-to-Point WAN Los Angeles

Chicago

Redundancy incurs both circuit and port costs Multiple-hop latency occurs in partial-mesh topologies

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Frame Relay: Cost-Effective Connectivity(6*5)/2 = 15 circuits

One access interface One logical hop to any point

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Frame Relay Access DevicesCarrier

FRAD

FRAD

Logical DTE to logical DCE Virtual circuits are end-to-end

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Frame Relay Service and CircuitsCIR 56 kbps—PVC DLCI 99 DLCI 86

64 kbps

1.5 Mbps

Data-link connection identifier (DLCI) Committed information rate (CIR) Access rate is 56 kbps, 64 kbps, or 1.544 Mbps

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Frame Relay Operation— SwitchingP0 Frame Relay Packet Header Data ... Frame Relay Switch P1 P2 Frame Relay Packet Header Data ...

P0 Switching Table DLCI = 100 IN_Port IN_DLCI OUT_Port OUT_DLCI P0 P0 100 350 P1 P2 200 275 DLCI = 200

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Frame Relay Operation—LMI Link Management Interface ANSI T1.617 Annex D ITU-T Q.933 Annex A Frame Relay Forum LMI

Frame Relay Switch

LMI- PVC status - Keepalives

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RFC 1490 Specifications for Frame Relay

Token Ring

Token Ring

Both bridged and routed traffic can be carried over Frame Relay

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Frame Relay MappingArriving Packet Forwarded Packet 10.0.0.0

Routing Table Network Address of Interface Next Router 10.0.0.0 172.16.1.2 Main Memory S0

Frame Relay Map Address of DLCI Next Router 172.16.1.2 100

Physical Interface

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Inverse ARP Eliminates manual configuration Router learns DLCI from switch Sends Inverse ARP request to each DLCIFrame Relay Switch

Frame Relay Map Address of Next Router 172.16.1.2 DLCI

P0 Switching Table IN_Port IN_DLCI OUT_Port OUT_DLCI P0 100 350 P1 P2 200 275

100 P0

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Interaction with Routing Protoco

lsSplit horizon prevents advertising of 10.0.0.0 or 12.0.0.0 10.0.0.0 Advertised No knowledge of 12.0.0.0 10.0.0.0 A C No knowledge of 10.0.0.0 Routing Table Network Interface 10.0.0.0 Serial 0 12.0.0.0 Serial 0 12.0.0.0 Advertised B 12.0.0.0

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NBMA Network Type Nonbroadcast multiaccess (NBMA) Frame Relay network is one subnet Full mesh required for full connectivityKnowledge of 12.0.0.0 10.0.0.0

S0

Knowledge of 10.0.0.0 12.0.0.0 One subnet

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Subinterfaces Single physical interface appears as multiple logical interfaces Overcomes split horizon Each subinterface is a separate subnetLogical subnet S0.1 Physical interface S0 Knowledge of 12.0.0.0 10.0.0.0

S0.2 Logical subnet

Knowledge of 10.0.0.0 12.0.0.0

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Topology Options Several topology options exist NBMA Subinterface with full mesh Subinterface with hub and spoke

Considerations Number of PVCs required Number of subnets required Number of hops required

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NBMA Using Full Mesh Considerations Number of PVC = 6 s Number of Subnets = 1 Number of Hops A -> = 1 B

A

B

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Subinterfaces Using Full Mesh Considerations Number of PVCs = 6 Number of Subnets = 6 Number of Hops A -> B = 1

A

B

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Subinterfaces Using Hub and Spoke Considerations Number of PVCs = 3 Number of Subnets = 3 Number of Hops A -> B = 2Hub site

A

B

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Dial-on-Demand as Backup for Frame Relay Use a floating static route Interesting packets initiate DDR when routing topology changesIGRP’s administrative distance is 100

HUB

Static route’s administrative distance is 200

HUB

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Cisco 思科 网络 技术 培训 文档

Summary Frame Relay provides a flexible, cost-effective method of connecting LANs over WAN links Frame Relay interaction with routing protocols must be considered Several topology options exist for Frame Relay designs

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