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Network Convergence: How Routes Propagate After Failure

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Convergence: the race from failure to recovery

When a network link fails, three things must happen: (1) detect the failure, (2) recalculate routes, (3) install new routes in forwarding tables. The time from failure to restored service is convergence time.

With default timers, OSPF convergence takes 40-90 seconds — during which users see the outage. With BFD and tuned timers, this drops to 1-3 seconds. With pre-computed backups (LFA/FRR), it drops to sub-50ms.

Packets in motion — click to inspect:

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