MPLS and RSVP
7210 SAS M, T, X, R6, Mxp MPLS Configuration Guide Page 23
previous hop router to this router (strict) or can traverse through other routers (loose).
You can control how the path is set up. They are similar to static LSPs but require less
configuration. See RSVP on page 60.
ā Constrained-path LSPs ā 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 which satisfies the constraints for the LSP. In turn,
CSPF relies on the topology database provided by the extended IGP such as OSPF or
IS-IS.
Once the path is found by CSPF, RSVP uses the path to request the LSP set up. CSPF
calculates the shortest path based on the constraints provided such as bandwidth, class
of service, and specified hops.
If fast reroute is configured, the ingress router signals the routers downstream. Each downstream
router sets up a detour for the LSP. If a downstream router does not support fast reroute, the
request is ignored and the router continues to support the LSP. This can cause some of the detours
to fail, but otherwise the LSP is not impacted.
No bandwidth is reserved for the rerouted 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 the LSP
backup LSP establishment.
Hop-limit parameters specifies the maximum number of hops that an LSP can traverse, including
the ingress and egress routers. An LSP is not set up if the hop limit is exceeded. The hop count is
set to 255 by default for the primary and secondary paths. It is set to 16 by default for a bypass or
detour LSP path.
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