What happens when an EIGRP route fails?

When an EIGRP route fails, the protocol has a built-in mechanism to ensure fast convergence by automatically selecting a new successor. EIGRP uses a concept known as feasible successors, which are backup routes that are pre-calculated and stored in the topology table. When the primary route (successor) to a destination becomes unavailable, EIGRP can quickly failover to one of these feasible successors without the need for a full recalculation of the routing table. This allows for minimal disruption and maintains network stability.

Furthermore, EIGRP's design allows it to maintain the state of its topology, so the failure of a route does not require all neighbors to reset their routing tables, interfaces to go down, or the routing entry to be immediately eradicated from the topology table. The ability to automatically switch to a backup route is one of EIGRP's strengths and is crucial for maintaining high availability in an enterprise network.