Why is fast convergence important in distance-vector routing protocols?

• A. To minimize downtime and reduce the chance of routing loops during topology changes.
• B. To maximize the frequency of updates regardless of network stability.
• C. To keep the routing table size small by delaying updates.
• D. To ensure all routers always have identical route tables.

Answer: (A)

Fast convergence in distance-vector routing is about how quickly every router settles on a consistent view of the network after a change. When a link or route fails or a new one comes up, each router must learn about that change from its neighbors and harmonize its routing table with the new reality. If convergence is slow, some routers keep using outdated paths while others have already switched, so traffic can be forwarded along routes that no longer work. This creates downtime and opens the door to routing loops, where packets circulate because routers haven’t all updated their information in step.

Speeding up convergence reduces the window during which inconsistent routing information exists, so packets are steered away from failed paths sooner and the network stabilizes faster. Techniques like triggered updates—sending immediate advertisements when a change happens—and route poisoning to mark invalid paths help achieve this, while mechanisms like hold-down timers trade off responsiveness for stability and can affect convergence time.

The other ideas—updating as often as possible regardless of stability, delaying updates to keep table sizes small, or always keeping identical tables—don’t capture the practical aim as well. Frequent updates without regard to stability wastes bandwidth and can cause flapping; delaying updates to shrink a table isn’t about finishing the convergence quickly; and while identical tables are the goal, achieving that quickly is what fast convergence is really about.