Link state

© 2002, Cisco Systems, Inc. All rights reserved.
© 2002, Cisco Systems, Inc. All rights reserved.
2
Link-State and Balanced Hybrid Routing
Objectives
Upon completing this lesson, you will be able to:
Describe the issues associated with link-state routing and identify solutions to those issues
Describe the features of balanced hybrid routing protocols
After initial flood, pass small event-triggered link-state
updates to all other routers
Link-State Routing Protocols
Minimizes routing table entries
Localizes impact of a topology change within
an area
Link-State Network Hierarchy Example
Link-State Routing
Protocol Algorithms
Benefits of Link-State Routing
Fast convergence: changes are reported immediately by the source affected.
Robustness against routing loops:
Routers know the topology.
Link-state packets are sequenced and acknowledged.
By careful (hierarchical) network design, you can utilize resources optimally.
Caveats of Link-State Routing
Significant demands for resources:
Memory (three tables: adjacency, topology, forwarding)
CPU (Dijkstra’s 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 complex
when tuning various parameters and when the design is complex
Troubleshooting easier than in distance vector routing
Drawbacks to Link-State Routing Protocols
Initial discovery may cause flooding.
Memory- and processor-intensive.
Shares attributes of both distance vector
and link-state routing
Balanced Hybrid Routing
Summary
Link-state routing uses LSAs, a topological database, the SPF algorithm, the resulting SPF tree, and a routing table of paths and ports to each network.
Link-state routing algorithms maintain a complex database of the network`s topology by exchanging LSAs with other routers in a network.
Link-state routing may flood the network with LSAs during initial topology discovery and can be both memory- and processor-intensive.
Balanced hybrid routing protocols combine aspects of both distance vector and link-state protocols.