RIP and IGRP Convergence
Convergence time is one of the problems associated with distance-vector protocols, such as RIPv1 and IGRP. When a router detects a link failure between itself and a neighbor, it sends a flash update with a poisoned route to it other neighbors. These neighbors in turn create a new flash update and send it to all of its neighbors, and so on. The Router that detected the link failure purges the entry for the failed link and removes all routes associated with that link from the routing table. The router then sends a query to its neighbors for the routs that have been removed. If a neighbor responds with a route, it is immediately installed in the routing table. The router does not go into hold-down because the entry was already purged. However, its neighbors are in hold-down for the failed route, thus ignoring periodic advertisement for that route. As the other routers come out of hold-down, the new route announced by the router that detected the failed link will cause their routing table entries to be updated.