Lsp Types - Nokia 7705 SAR-W Series Manual

MPLS and RSVP-TE
Static LSPs can cross AS boundaries. The intermediate hops are manually
configured so that the LSP has no dependence on the IGP topology or a local
forwarding table.

3.2.5 LSP Types

The following LSP types are supported:
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
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• 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
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
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.
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Label Distribution
RSVP and RSVP-TE. An explicit path that has not
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Protocol.
RSVP-TE Fast Reroute
3HE 18686 AAAB TQZZA
MPLS Guide
(FRR).