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Routing & Switching · Intermediate

Route Poisoning

Advertising a failed route with an infinite metric so neighbors immediately remove it instead of waiting for it to age out.

Definition

When a distance-vector router loses a route, it advertises the route with an unreachable metric, such as 16 hops in RIP or a delay of infinity in EIGRP. Neighbors then mark the route invalid, speeding convergence and preventing count-to-infinity loops.

Example

A RIP router advertises 10.5.0.0/16 with metric 16 after its interface fails.

Exam tip

In RIP, a metric of 16 equals unreachable; route poisoning uses that value.

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