Rsvp-Te Lsp Shortcut For Igp Resolution - Alcatel-Lucent 7950 SR User Configuration Manual

Advanced MPLS/RSVP Features

RSVP-TE LSP Shortcut for IGP Resolution

RSVP-TE LSP shortcut for IGP route resolution allows forwarding of packets to IGP learned
routes using an RSVP-TE LSP. This is also referred to as IGP shortcut. This feature is enabled by
entering the following command at the IS-IS routing protocol level or at the OSPF routing
protocol instance level:
•
•
These commands instruct IS-IS or OSPF to include RSVP LSPs originating on this node and
terminating on the router-id of a remote node as direct links with a metric equal to the operational
metric provided by MPLS. If the user enabled the relative-metric option for this LSP, IGP will
apply the shortest IGP cost between the endpoints of the LSP plus the value of the offset, instead
of the LSP operational metric, when computing the cost of a prefix which is resolved to the LSP.
When a prefix is resolved to a tunnel next-hop, the packet is sent labeled with the label stack
corresponding to the NHLFE of the RSVP LSP. Any network event causing an RSVP LSP to go
down will trigger a full SPF computation which may result in installing a new route over another
RSVP LSP shortcut as tunnel next-hop or over a regular IP next-hop.
When rsvp-shortcut is enabled at the IGP instance level, all RSVP LSPs originating on this node
are eligible by default as long as the destination address of the LSP, as configured in config-
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:
•
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
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config>router>isis>rsvp-shortcut
config>router>ospf>rsvp-shortcut
config>router>mpls>lsp>no igp-shortcut
7950 SR OS MPLS Configuration Guide