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Routing & Switching · Advanced

Incremental SPF (iSPF)

An optimization where only the affected portion of the SPF tree is recalculated after a change.

Definition

Rather than rerunning Dijkstra over the whole LSDB, iSPF recomputes from the point of change, reducing CPU and convergence time in large areas. It benefits most when changes are far from the computing router.

Example

ispf under router ospf 1

Exam tip

iSPF reduces SPF computation, not flooding; LSA throttling handles flooding rate.

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