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2002, Cisco Systems, Inc. All rights reserved. ICND v2.05-3

Objectives

Upon completing this lesson, you will beable to:

Describe the issues associated with link-staterouting and identify solutions to those issues

Describe the features of balanced hybrid routingprotocols

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After initial flood, pass small event-triggered link-state

updates to all other routers

Link-State Routing Protocols

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Minimizes routing table entries

Localizes impact of a topology change within

an area

Link-State Network HierarchyExample

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Link-State RoutingProtocol Algorithms

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Benefits of Link-State Routing

Fast convergence: changes are reportedimmediately by the source affected.

Robustness against routing loops:Routers know the topology.

Link-state packets are sequenced andacknowledged.

By careful (hierarchical) network design, youcan utilize resources optimally.

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Caveats of Link-State Routing

Significant demands for resources:

Memory (three tables: adjacency, topology, forwarding)

CPU (Dijkstras algorithm can be intensive, especially

when a lot of instabilities are present.) Requires very strict network design (when more areas

area routing)

Problems with partitioning of areas

Configuration generally simple but can be complexwhen tuning various parameters and when the design iscomplex

Troubleshooting easier than in distance vector routing

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Drawbacks to Link-State RoutingProtocols

Initial discovery may cause flooding.

Memory- and processor-intensive.

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Shares attributes of both distance vectorand link-state routing

Balanced Hybrid Routing

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Summary

Link-state routing uses LSAs, a topologicaldatabase, the SPF algorithm, the resulting SPF tree,and a routing table of paths and ports to eachnetwork.

Link-state routing algorithms maintain a complexdatabase of the network's topology by exchangingLSAs with other routers in a network.

Link-state routing may flood the network with LSAs

during initial topology discovery and can be bothmemory- and processor-intensive.

Balanced hybrid routing protocols combine aspectsof both distance vector and link-state protocols.

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