MPLS Guide MPLS and RSVP-TE
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CSPF must be enabled for fast reroute to work. If an LSP is configured with fast-reroute frr-
method specified but does not enable CSPF, neither global revertive nor local revertive will
be available for the LSP to recover.
The one-to-one fast reroute method creates a separate detour LSP for each backed-up LSP.
One-to-one is not supported for LSP templates.
The facility fast reroute method, sometimes called many-to-one, takes advantage of the
MPLS label stack. Instead of creating a separate LSP for every backed-up LSP, a single LSP
is created that serves to back up a set of LSPs. This LSP tunnel is called a bypass tunnel.
The bypass tunnel must intersect the path of the original LSPs somewhere downstream of
the point of local repair (PLR). This constrains the set of LSPs being backed up via that
bypass tunnel to those LSPs that pass through a common downstream node. All LSPs that
pass through the PLR and through this common node that do not also use the facilities
involved in the bypass tunnel are candidates for this set of LSPs.
The no form of the fast-reroute command removes the protection LSP from each node on
the primary path. This command will also remove configuration information about the hop-
limit and the bandwidth for the detour routes.
Default no fast-reroute
Parameters frr-method — specifies the fast reroute method to use
Values one-to-one, facility
Default one-to-one
hop-limit
Syntax hop-limit limit
no hop-limit
Context config>router>mpls>lsp>fast-reroute
config>router>mpls>lsp-template>fast-reroute
Description For fast reroute, this command defines how many more routers a protection tunnel is allowed
to traverse compared with the LSP itself. For example, if an LSP traverses four routers, any
protection tunnel for the LSP can be no more than 10 router hops, including the ingress and
egress routers.
The no form of the command reverts to the default value.
Default 16
Parameters limit — specifies the maximum number of hops
Values 0 to 255
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