The following LSP types are supported:
static LSPs — a static LSP specifies a static path. All routers that the LSP traverses must be configured manually with labels. No RSVP-TE or LDP signaling is required. Static LSPs are discussed in this chapter.
signaled LSPs — LSPs are set up using the RSVP-TE or LDP signaling protocol. The signaling protocol allows labels to be assigned from an ingress router to the egress router. Signaling is triggered by the ingress routers. Configuration is required only on the ingress router and is not required on intermediate routers. Signaling also facilitates path selection. RSVP-TE is discussed in this chapter, and LDP is discussed in Label Distribution Protocol.
There are two types of signaled LSP:
explicit-path LSPs — MPLS uses RSVP-TE to set up explicit-path LSPs. The hops within the LSP are configured manually. The intermediate hops must be configured as either strict or loose, meaning that the LSP must take either a direct path from the previous hop router to this router (strict) or can traverse other routers (loose). This enables the user to control how the path is set up. Explicit-path LSPs are similar to static LSPs but require less configuration. See RSVP and RSVP-TE. An explicit path that has not specified any hops will follow the IGP route.
constrained-path LSPs — for constrained-path LSPs, the intermediate hops of the LSP are dynamically assigned. A constrained-path LSP relies on the Constrained Shortest Path First (CSPF) routing algorithm to find a path that satisfies the constraints for the LSP. In turn, CSPF relies on the topology database provided by an extended IGP such as OSPF or IS-IS.
Once the path is found by CSPF, RSVP-TE uses the path to request the LSP setup. CSPF calculates the shortest path based on the constraints provided, such as bandwidth, class of service, and specified hops.
If Fast Reroute (FRR) is configured, the ingress router signals the downstream routers so that each downstream router can preconfigure a detour route for the LSP that will be used if there is a failure on the original LSP. If a downstream router does not support FRR, the request is ignored and the router continues to support the original LSP. This can cause some of the detour routes to fail, but the original LSP is not impacted. For more information on FRR, see RSVP-TE Fast Reroute (FRR).
No bandwidth is reserved for the reroute path. If the user enters a value in the bandwidth parameter in the config>router>mpls>lsp>fast-reroute context, it will have no effect on establishing the backup LSP. The following warning message is displayed:
‟The fast reroute bandwidth command is not supported in this release.”