Question

A network engineer troubleshoots a hub-and-spoke topology where RIPv2 runs on all links. Users report that a route to 10.20.5.0/24 sometimes takes 3+ minutes to be removed from the routing tables after the destination fails. On R2 (a transit router), the command 'show ip protocols' confirms RIP is enabled, and 'debug ip rip' shows R2 advertising 10.20.5.0/24 back out the same interface it learned the route on, with a metric of 16. Which RIP loop-prevention mechanism is producing this behavior, and what is its purpose?

Accepted Answer

Poison reverse — it advertises the failed route back toward the source with an infinite (16) metric to explicitly override split horizon and speed removal of the unreachable route

Answer

Split horizon — it prevents R2 from ever advertising a route out the interface it was learned on, so the metric-16 update indicates a misconfiguration

Answer

Route tagging — R2 is tagging the route as external so downstream routers filter it, but the tag value 16 is invalid

Answer

Holddown timer — the metric-16 advertisement starts a holddown that suppresses the route for 180 seconds, which cannot be shortened