Network Design and Operations
Which statement correctly describes a link-state routing protocol?
- AEach router builds its routing table only from the destinations and distances (such as hop counts) it receives from neighboring routers
- BEach router floods the state of its own links so that all routers share the topology of the whole network, and each router computes shortest paths with Dijkstra's algorithm
- CAn administrator configures routes on each router by hand, and routers exchange no routing information
Show answer and explanation
Answer: B. Each router floods the state of its own links so that all routers share the topology of the whole network, and each router computes shortest paths with Dijkstra's algorithm
In a link-state protocol (such as OSPF or IS-IS), each router advertises the state of its links (its neighbors and the costs to them), and all routers in the same area hold the same map. From this map, each router computes a shortest-path tree rooted at itself with Dijkstra's algorithm. A distance-vector protocol (such as RIP) chooses routes by adding its own distance to the "distance to each destination" heard from its neighbors; this is simple, but routers do not know the topology of the whole network and can take time to settle after a failure. Link-state protocols need more computation and memory but react to changes quickly.
- A. This describes a distance-vector protocol.
- B. Correct. Routers share the whole topology and each computes the shortest paths.
- C. This describes static routing.