CSPF

constrained shortest path first

CSPF is a component of constraint-based routing that uses a TED to find the shortest path through an MPLS domain that meets established constraints. The ingress router determines the physical path for each LSP by applying the CSPF algorithm to the TED information. Input to the CSPF algorithm includes topology link-state information learned from the IGP, LSP administrative attributes, and network resource attributes that are carried by IGP extensions and stored in the TED.

As CSPF considers each candidate NE and link for a new LSP, it accepts or rejects a specific path component based on resource availability and whether selecting the component violates policy constraints. The output of the CSPF calculation is an explicit route that consists of a sequence of router addresses. The explicit route is passed to the signaling component, which establishes forwarding states in the routers along the LSP.