Another method routers use for routing loop prevention is to never advertise a route back to a router from which it was learned. What is this called?

• A. Split Horizon
• B. Route Poisoning
• C. Hold Down
• D. Route Filtering

Answer: (A)

Split horizon is a loop-prevention technique in distance-vector routing. The router, when it learns a route on one interface, does not advertise that same route back out the interface it came from. This stops routing information from bouncing between neighbors and creating a loop.

Route poisoning marks a failed route with an infinite metric so neighbors learn it’s unreachable; hold-down timers suppress rapid changes after a route failure to prevent flaps; route filtering uses access controls to block certain routes from being advertised or accepted. The behavior described—not advertising a learned route back to the sender—fits split horizon.