Weighted Load-Balancing over MPLS LSP
60 Router Configuration Guide
Interaction with BGP Route Resolution to an LDP FEC
There is no interaction between an LDP shortcut for BGP next-hop resolution and the LDP
shortcut for IGP route resolution. BGP will continue to resolve a BGP next-hop to an LDP
shortcut if the user enabled the following option in BGP:
config>router>bgp>next-hop-resolution>shortcut-tunnel
family ipv4
resolution-filter ldp
Interaction with Static Route Resolution to an LDP FEC
A static route will continue to be resolved by searching an LDP LSP which FEC prefix
matches the specified indirect next-hop for the route. In contrast, the LDP shortcut for IGP
route resolution uses the LDP LSP as a route. The most specific route for a prefix will be
selected and if both a static and IGP routes exist, the RTM route type preference will be used
to select one.
LDP Control Plane
In order for the LDP shortcut to be usable, an SR OS router must originate a <FEC, label>
binding for each IGP route it learns of even if it did not receive a binding from the next-hop
for that route. In other words, it must assume it is an egress LER for the FEC until the route
disappears from the routing table or the next-hop advertised a binding for the FEC prefix. In
the latter case, the SR OS router becomes a transit LSR for the FEC.
An SR OS router will originate a <FEC, label> binding for its system interface address only
by default. The only way to originate a binding for local interfaces and routes which are not
local to the system is by using the fec-originate capability.
You must use the fec-originate command to generate bindings for all non-local routes for
which this node acts as an egress LER for the corresponding LDP FEC. Specifically, this
feature must support the FEC origination of IGP learned routes and subscriber/host routes
statically configured or dynamically learned over subscriber IES interfaces.
An LDP LSP used as a shortcut by IPv4 packets may also be tunneled using the LDP-over-
RSVP feature.
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