What is convergence in routing protocols, and why is fast convergence desirable?

• A. Routers gradually update the routing table only during maintenance windows.
• B. All routers have consistent routing tables; faster convergence reduces downtime and routing loops.
• C. Convergence is when BGP peers exchange AS path information; faster convergence reduces memory usage.
• D. Convergence means all routes have zero metric; faster convergence increases route flaps.

Answer: (B)

Convergence in routing protocols means that after a topology change, all routers settle on a single, consistent view of the network and agree on the best paths. Fast convergence is desirable because it minimizes the time the network spends with inconsistent routing information, which reduces downtime and the chance of routing loops. When convergence happens quickly, traffic is quickly redirected onto valid, loop-free paths, with less packet loss and latency. The correct idea is that routers end up with a consistent set of routes, and speeding up that process reduces both downtime and potential loops. The other statements don’t describe convergence accurately—for example, maintenance windows aren’t about how convergence works, AS-path exchange and memory usage aren’t the general meaning of convergence, and zero metrics don’t define convergence either.