As shown in the figure, there are several advantages of link-state routing protocols compared to distance vector routing protocols.
- Builds a Topological Map - Link-state routing protocols create a topological map, or SPF tree of the network topology. Because link-state routing protocols exchange link-states, the SPF algorithm can build an SPF tree of the network. Using the SPF tree, each router can independently determine the shortest path to every network.
- Fast Convergence - When receiving an LSP, link-state routing protocols immediately flood the LSP out all interfaces except for the interface from which the LSP was received. In contrast, RIP needs to process each routing update and update its routing table before flooding them out other interfaces.
- Event-driven Updates - After the initial flooding of LSPs, link-state routing protocols only send out an LSP when there is a change in the topology. The LSP contains only the information regarding the affected link. Unlike some distance vector routing protocols, link-state routing protocols do not send periodic updates.
- Hierarchical Design - Link-state routing protocols use the concept of areas. Multiple areas create a hierarchical design to networks, allowing for better route aggregation (summarization) and the isolation of routing issues within an area.
Link-state protocols also have a few disadvantages compared to distance vector routing protocols:
- Memory Requirements - Link-state protocols require additional memory to create and maintain the link-state database and SPF tree.
- Processing Requirements - Link-state protocols can also require more CPU processing than distance vector routing protocols. The SPF algorithm requires more CPU time than distance vector algorithms such as Bellman-Ford, because link-state protocols build a complete map of the topology.
- Bandwidth Requirements - The flooding of link-state packets can adversely affect the available bandwidth on a network. This should only occur during initial startup of routers, but can also be an issue on unstable networks.