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Routing & Switching · Foundational

Convergence

The state in which all routers have consistent, accurate routing information after a topology change.

Definition

Convergence time includes failure detection, propagation of the change, route recomputation and FIB update. Link-state protocols and EIGRP converge much faster than RIP, and features such as BFD, fast hellos, LFA and TI-LFA reduce convergence further. During convergence, transient loops or blackholes may occur.

Example

BFD detects a failed link in 150 ms, allowing OSPF to reconverge in under a second.

Exam tip

Faster timers improve convergence but increase CPU load; BFD is usually the preferred answer for fast failure detection.

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