RSVP-TE LSP Shortcut for IGP Resolution
Page 128 7450 ESS MPLS Guide
ure>router>mpls>lsp>to, corresponds to a router-id of a remote node. RSVP LSPs with a
destination corresponding to an interface address or any other loopback interface address of a
remote node are automatically not considered by IS-IS or OSPF. The user can, however, exclude a
specific RSVP LSP from being used as a shortcut for resolving IGP routes by entering the
command:
• config>router>mpls>lsp>no igp-shortcut
It is specifically recommended to disable igp-shortcut option on RSVP LSP which has the cspf
option disabled unless the full explicit path of the LSP is provided in the path definition. MPLS
tracks in RTM the destination or the first loose-hop in the path of a non CSPF LSP and as such this
can cause bouncing when used within IGP shortcuts.The SPF in OSPF or IS-IS will only use
RSVP LSPs as forwarding adjacencies, IGP shortcuts, or as endpoints for LDP-over-RSVP. These
applications of RSVP LSPs are mutually exclusive at the IGP instance level. If the user enabled
two or more options in the same IGP instance, then forwarding adjacency takes precedence over
the shortcut application that takes precedence over the LDP-over-RSVP application.
Table 7 summarizes the outcome in terms of RSVP LSP role of mixing these configuration
options.
Table 7: RSVP LSP Role As Outcome of LSP level and IGP level configuration options
IGP Instance level configurations
LSP level
configuration
advertise-
tunnel-link
enabled /
rsvp-short-
cut enabled /
ldp-over-
rsvp enabled
advertise-
tunnel-link
enabled /
rsvp-short-
cut enabled /
ldp-over-
rsvp dis-
abled
advertise-
tunnel-link
enabled /
rsvp-short-
cut disabled
/ ldp-over-
rsvp dis-
abled
advertise-
tunnel-link
disabled /
rsvp-short-
cut disabled
/ ldp-over-
rsvp dis-
abled
advertise-
tunnel-link
disabled /
rsvp-short-
cut enabled /
ldp-over-
rsvp enabled
advertise-
tunnel-link
disabled /
rsvp-short-
cut disabled
/ ldp-over-
rsvp enabled
igp-shortcut
enabled / ldp-
over-rsvp
enabled
Forwarding
Adjacency
Forwarding
Adjacency
Forwarding
Adjacency
None IGP
Shortcut
LDP-over-
RSVP
igp-shortcut
enabled / ldp-
over-rsvp dis-
abled
Forwarding
Adjacency
Forwarding
Adjacency
Forwarding
Adjacency
None IGP
Shortcut
None
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