What is split horizon, and what is its role in preventing routing loops?

• A. Split horizon prevents a router from advertising a route back out the same interface it was learned on.
• B. Split horizon accelerates convergence by flooding routes to all neighbors.
• C. Split horizon enforces route summarization at network borders.
• D. Split horizon requires manual configuration to take effect.

Answer: (A)

Split horizon is a rule used by distance-vector routing protocols that prevents a router from advertising a learned route back out the same interface it was received on. This stops information from bouncing back and forth between two routers on the same link, which can create routing loops. By not re-sending the update on that interface, the network avoids the situation where a route keeps circulating and confusing neighbors about the best path. Some implementations use split horizon with poison reverse, which explicitly advertises the route back with an infinite metric to force the other side to remove it. In contrast, options that claim it floods to all neighbors, enforces route summarization at borders, or requires manual configuration do not describe how split horizon works to prevent loops.