What happens when a router’s link fails in RIP?

When a router's link fails while using the Routing Information Protocol (RIP), it marks the route associated with that link as unreachable by setting its hop count to 16. In RIP, a hop count of 16 is considered to indicate an unreachable route, as RIP is designed to support a maximum hop count of 15.

This mechanism allows other routers in the network to recognize that the failed route is no longer valid. By advertising the route with a hop count of 16 to its neighbors, the router effectively informs them that the destination is inaccessible, helping to prevent routing loops and ensuring the stability of the routing environment.

Marking routes as unreachable is a critical part of RIP's distance vector protocol, which relies on periodic updates to communicate routing information among routers. This approach ensures that all active routers eventually converge on an updated view of the network, reflecting any changes due to link failures or changes in network topology.