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LDP Shortcut for BGP Next-Hop Resolution
LDP shortcut for BGP next-hop resolution shortcuts allow for the deployment of a 'route-less
core' infrastructure. Many service providers either have or intend to remove the IBGP mesh from
their network core, retaining only the mesh between routers connected to areas of the network that
require routing to external routes.
Shortcuts are implemented by utilizing Layer 2 tunnels (i.e., MPLS LSPs) as next hops for
prefixes that are associated with the far end termination of the tunnel. By tunneling through the
network core, the core routers forwarding the tunnel have no need to obtain external routing
information and are immune to attack from external sources.
The tunnel table contains all available tunnels indexed by remote destination IP address. LSPs
derived from received LDP /32 route FECs will automatically be installed in the table associated
with the advertising router-ID when IGP shortcuts are enabled.
Evaluating tunnel preference is based on the following order in descending priority:
1. LDP /32 route FEC shortcut
2. Actual IGP next-hop
If a higher priority shortcut is not available or is not configured, a lower priority shortcut is
evaluated. When no shortcuts are configured or available, the IGP next-hop is always used.
Shortcut and next-hop determination is event driven based on dynamic changes in the tunneling
mechanisms and routing states.
Refer to the 7950 SR OS Routing Protocols Guide for details on the use of LDP FEC and RSVP
LSP for BGP Next-Hop Resolution.
7950 SR OS MPLS Configuration Guide
Label Distribution Protocol
Page 367
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