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Routing & Switching · Advanced

Constrained Shortest Path First (CSPF)

A modified SPF that prunes links not meeting constraints (bandwidth, affinity, SRLG) before computing a path.

Definition

CSPF runs on TE headends or PCEs using the TE database flooded by the IGP. It returns an explicit path that RSVP-TE or SR-TE then signals or encodes.

Example

A tunnel requiring 500 Mbps excludes links with less unreserved bandwidth.

Exam tip

CSPF computes; RSVP-TE signals.

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