Alcatel-Lucent 7450 Configuration Manual page 57

config>router>ldp-shortcut [ipv4] [ipv6]
IGP Route Resolution
When LDP shortcut is enabled, LDP populates the RTM with next-hop entries corresponding
to all prefixes for which it activated an LDP FEC. For a given prefix, two route entries are
populated in RTM. One corresponds to the LDP shortcut next-hop and has an owner of LDP.
The other one is the regular IP next-hop. The LDP shortcut next-hop always has preference
over the regular IP next-hop for forwarding user packets and specified control packets over a
given outgoing interface to the route next-hop.
The prior activation of the FEC by LDP is done by performing an exact match with an IGP
route prefix in RTM. It can also be done by performing a longest prefix-match with an IGP
route in RTM if the aggregate-prefix-match option is enabled globally in LDP ldp-interarea-
prd.
The LDP next-hop entry is not exported to LDP control plane or to any other control plane
protocols except OSPF, IS-IS, and specific OAM control plane as specified in
Control
This feature is not restricted to /32 IPv4 prefixes or /128 IPv6 FEC prefixes. However only /
32 IPv4 and /128 IPv6 FEC prefixes will be populated in the Tunnel Table for use as a tunnel
by services.
All user and specified control packets for which the longest prefix match in RTM yields the
FEC prefix will be forwarded over the LDP LSP. The following is an example of the
resolution process.
Assume the egress LER advertised a FEC for some /24 prefix using the fec-originate
command. At the ingress LER, LDP resolves the FEC by checking in RTM that an exact
match exists for this prefix. Once LDP activated the FEC, it programs the NHLFE in the
egress data path and the LDP tunnel information in the ingress data path tunnel table.
Next, LDP provides the shortcut route to RTM which will associate it with the same /24
prefix. There will be two entries for this /24 prefix, the LDP shortcut next-hop and the regular
IP next-hop. The latter was used by LDP to validate and activate the FEC. RTM then resolves
all user prefixes which succeed a longest prefix match against the /24 route entry to use the
LDP LSP.
Router Configuration Guide
Packets.
IP Router Configuration
Handling of
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