linkstate

Link-state is a class of routing protocol in which each router builds a complete map of the network's topology to determine the best paths. In a link-state routing protocol, every router advertises its directly connected links and their costs through link-state advertisements (LSAs). These LSAs are flooded reliably to all routers in the routing domain, so each router maintains a link-state database (LSDB) containing the topology of the entire area.

To compute routes, each router runs a shortest-path algorithm, typically Dijkstra's algorithm, on the LSDB to produce a shortest-path tree rooted at itself. The first hop toward any destination is based on the successor in that tree.

Examples include OSPF and IS-IS. OSPF uses areas to confine LSDBs and LSAs, improving scalability, while IS-IS organizes networks into a two-level hierarchy.

Link-state protocols generally converge quickly and avoid routing loops, but they require more memory and CPU than distance-vector protocols and more complex configuration.

Direct benefits: fast convergence, accurate routing, scalable in moderate to large networks. Drawbacks: higher overhead for LSA flooding, need for reliable flood and authentication to prevent spoofing. Metrics are typically costs associated with links (such as bandwidth).

Compared with distance-vector protocols like RIP, link-state protocols maintain a complete network map and compute routes independently at each router, reducing count-to-infinity problems and enabling more sophisticated route selection.