What is route flapping and a common mitigation technique?

• A. Frequent rapid changes in routes causing instability; mitigated with dampening.
• B. Routes changing only at long intervals; mitigated with faster timers.
• C. Routes never change; mitigated with static routes.
• D. Convergence is slowed; mitigated with route filtering.

Answer: (A)

Route flapping is when routes rapidly switch between being available and unavailable, causing the routing table to churn and routers to repeatedly recompute paths. This instability can waste CPU and memory and disrupt traffic.

Dampening is a common way to mitigate it. It works by assigning a penalty each time a route flaps (updates/withdrawals). If the penalty crosses a threshold, the route is suppressed for a period, reducing announcements and churn. Over time, the penalty decays, and the route can reappear only when things have stabilized. This directly tackles the burstiness of flaps and smooths routing behavior.

The other ideas don’t fit as well: changes only at long intervals would indicate stability rather than flapping; routes never changing is the opposite of flapping; and route filtering addresses policy or security concerns, not the underlying instability from frequent route changes.