What mechanism helps prevent rapid changes in a route when a route becomes unstable?

• A. Split Horizon
• B. Route Poisoning
• C. ECMP
• D. Hold-Down Timers

Answer: (D)

Hold-down timers dampen route changes after a route instability by delaying how quickly a router updates or reuses a destination’s path. When a route is considered unreachable, the router marks it invalid and starts a hold-down timer. During that period, updates that would reintroduce the route or switch to another path aren’t acted on, which stops rapid back-and-forth changes as the network converges. This keeps the routing table stable and avoids flapping.

Other mechanisms have different purposes: Split Horizon helps prevent loops by not advertising a route back out the same interface; Route Poisoning instantly declares a route unreachable to speed convergence; ECMP distributes traffic across multiple equal-cost paths and doesn’t address the timing of accepting updates after instability. Hold-down timers specifically provide the stability during convergence.