MPLS Guide MPLS and RSVP-TE
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Next, the user must associate the LSP template with the previously defined route
policy, and this is accomplished using the auto-lsp lsp-template command:
config>router>mpls>auto-lsp lsp-template template-name policy peer-prefix-
policy
Once the auto-lsp lsp-template command is entered, the system starts the process
of establishing the point-to-point LSPs. The prefixes defined in the prefix list are
checked, and if a prefix corresponds to a router ID that is present in the Traffic
Engineering (TE) database, the system instantiates a CSPF-computed primary path
to that prefix using the parameters specified in the LSP template.
Multiple templates can be associated with the same or different peer prefix policies.
Each application of an LSP template with a given prefix in the prefix list results in the
instantiation of a single CSPF-computed LSP primary path using the LSP template
parameters, as long as the prefix corresponds to a router ID for a node in the TE
database. Auto LSP does not support the automatic signaling of a secondary path
for an LSP. If the signaling of multiple LSPs to the same destination node is required,
a separate LSP template must be associated with a prefix list that contains the same
destination node address. Each instantiated LSP will have a unique LSP ID and a
unique tunnel ID.
The auto-created LSP is installed in the Tunnel Table Manager (TTM) and is
available to applications such as resolution of BGP label routes, and resolution of
BGP, IGP, and static routes. The auto-created LSP can also be used for auto-binding
by a VPRN service. The auto-created LSP cannot be used as a provisioned SDP for
explicit binding by services.
The auto-created LSP mesh can be signaled over both numbered and unnumbered
RSVP-TE interfaces.
Up to five peer prefix policies can be associated with an LSP template. Every time
the user executes the auto-lsp command with the same or different prefix policy
associations or changes the prefix policy associated with an LSP template, the
system re-evaluates the prefix policy. The outcome of the re-evaluation indicates to
MPLS whether an existing LSP must be torn down or a new LSP must be signaled
to a destination address that is already in the TE database.
If a /32 prefix is added to or removed from a prefix list associated with an LSP
template, or if a prefix range is expanded or narrowed, the prefix policy re-evaluation
is performed. Whether the prefix list contains one or more specific /32 addresses or
a range of addresses, MPLS requires an external trigger to instantiate an LSP to a
node whose address matches an entry in the prefix list. The external trigger is when
the router with a router ID matching an address in the prefix list appears in the TE
database. The TE database provides the trigger to MPLS.
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