MPLS and RSVP
7450 ESS MPLS Guide Page 131
All control plane packets that require an RTM lookup and whose destination is reachable over the
RSVP shortcut will be forwarded over the shortcut. This is because RTM keeps a single route
entry for each prefix unless there is ECMP over different outgoing interfaces.
Interface bound control packets are not impacted by the RSVP shortcut since RSVP LSPs with a
destination address different than the router-id are not included by IGP in its SPF calculation.
Forwarding Adjacency
The forwarding adjacency feature can be enabled independently from the IGP shortcut feature in
CLI. To enable forwarding adjacency, the user enters the following command in IS-IS or OSPF:
• configure>router>isis>advertise-tunnel-link
• configure>router>ospf>advertise-tunnel-link
If both rsvp-shortcut and advertise-tunnel-link options are enabled for a given IGP instance,
then the advertise-tunnel-link will win. With this feature, ISIS or OSPF advertises an RSVP LSP
as a link so that other routers in the network can include it in their SPF computations. The RSVP
LSP is advertised as an unnumbered point-to-point link and the link LSP/LSA has no Traffic
Engineering opaque sub-TLVs as per RFC 3906 Calculating Interior Gateway Protocol (IGP)
Routes Over Traffic Engineering Tunnels.
The forwarding adjacency feature can be enabled independently from the IGP shortcut feature in
CLI. If both rsvp-shortcut and advertise-tunnel-link options are enabled for a given IGP instance,
then the advertise-tunnel-link will win.
When the forwarding adjacency feature is enabled, each node advertises a p2p unnumbered link
for each best metric tunnel to the router-id of any endpoint node. The node does not include the
tunnels as IGP shortcuts in SPF computation directly. Instead, when the LSA/LSP advertising the
corresponding P2P unnumbered link is installed in the local routing database, then the node
performs an SPF using it like any other link LSA/LSP. The link bi-directional check requires that a
link, regular link or tunnel link, exists in the reverse direction for the tunnel to be used in SPF.
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