Multiple choice

How does route poisoning prevent routing loops?

  1. New routing updates are ignored until the network has converged.

  2. Failed routes are advertised with a metric of infinity.

  3. A route is marked as unavailable when its Time to Live is exceeded.

  4. The unreachable route is cleared from the routing table after the invalid timer expires.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Route poisoning advertises failed routes with an infinite metric (option B), preventing other routers from using the bad route. This works with hold-down timers to prevent routing loops. Option A describes holddown, not poisoning. Option C describes TTL-based route expiration. Option D describes garbage collection. Route poisoning specifically marks failed routes as unreachable by advertising them with maximum metric.

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