1. © 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—3-1 Determining IP Routes Introducing Link-State and Balanced Hybrid Routing

2. © 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—3-2 Outline Overview How Routing Information Is Maintained with Link State Link-State Routing Protocol Algorithms Benefits and Limitations of Link-State Routing When to Use Link-State Routing Protocols Balanced Hybrid Routing Summary

3. © 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—3-3 After initial flood of LSAs, link-state routers pass small event-triggered link-state updates to all other routers. Link-State Routing Protocols

4. © 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—3-4 Minimizes routing table entries Localizes impact of a topology change within an area Link-State Network Hierarchy Example

5. © 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—3-5 Link-State Routing Protocol Algorithms

6. © 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—3-6 Benefits of Link-State Routing Fast convergence: –Changes are reported immediately by the affected source. Robustness against routing loops: –Routers know the topology. –Link-state packets are sequenced and acknowledged. Through careful (hierarchical) network design, resources can be optimized.

7. © 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—3-7 Caveats to Link-State Routing Significant demands for resources: –Memory (three tables: adjacency, topology, forwarding) –CPU (Dijkstra’s algorithm can be intensive, especially when many instabilities are present) Requires very strict network design Problems with partitioning of areas Configuration generally simple, but can be complex when tuning various parameters and when design is complex Troubleshooting easier than in distance vector routing

8. © 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—3-8 Drawbacks to Link-State Routing Protocols Initial discovery may cause flooding. Link-state routing is memory- and processor-intensive.

9. © 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—3-9 Shares attributes of both distance vector and link-state routing Balanced Hybrid Routing

10. © 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—3-10 Summary Link-state routing protocols collect routing information from all other routers in the network. After all information is collected, each router calculates its own best path to all destinations in the network. Link-state algorithms maintain a complex database of the network topology. Knowledge of the network routers and of how they interconnect is achieved through the exchange of LSAs with other routes in a network. Using triggered, flooded updates, link-state protocols can immediately report changes in the network topology, leading to fast convergence times. In contrast, the use of many different databases can require a significant amount of memory.

11. © 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—3-11 Summary (Cont.) To avoid an excessive use of memory, a strict hierarchical network design is required. The configuration of link-state networks should remain simple to avoid tuning. Balanced hybrid routing protocols combine aspects of both distance vector and link-state protocols.

12. © 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—3-12