Which feature enables the use of multiple equal-cost routes to a destination?

• A. Split Horizon
• B. Hold-Down Timers
• C. Route Poisoning
• D. Equal-Cost Multipath (ECMP)

Answer: (D)

Equal-Cost Multipath (ECMP) enables a router to use several routes that share the same cost to reach a destination. When multiple next-hops have identical metrics, the router can install all of them and distribute traffic across these equal-cost paths. This improves load balancing, increases throughput, and adds redundancy—if one path falters, traffic can continue over the others. In practice, ECMP relies on the routing protocol advertising multiple equal-cost paths and the router’s forwarding plane choosing a next-hop based on a hashing or per-flow strategy to spread traffic.

The other mechanisms address different issues. Split Horizon helps prevent routing loops by not advertising a route back out the interface it came from. Hold-down timers slow down the acceptance of changes to a route to avoid flapping. Route Poisoning marks a failed route with an infinite metric to quickly propagate failure. None of these enable using multiple equal-cost paths, which is the role of ECMP.