What is the primary purpose of route poisoning in IP routing?

• A. Increases routing speed
• B. Prevents routing loops
• C. Encrypts routing updates
• D. Discovers neighbors

Answer: (B)

Route poisoning is a technique used in routing protocols to prevent routing loops when a route becomes unavailable. When a router detects that a path to a destination is no longer reachable, it propagates that information by advertising the destination with an infinite metric. This tells neighboring routers that the route is unusable, causing them to remove it from their routing tables and to recompute alternative paths. By effectively marking the route as unreachable, the network converges more quickly and avoids the count-to-infinity problem that can happen when updates propagate slowly. It’s specifically about ensuring that failed routes aren’t propagated as valid paths, rather than speeding up routing, encrypting updates, or discovering neighbors.