Alcatel-Lucent 7450 Configuration Manual page 173

Description
This command enables the resolution of IGP routes using LDP LSP across all network interfaces
participating in the IS-IS and OSPF routing protocol in the system.
When LDP shortcut is enabled, LDP populates the routing table 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 the system routing table. One route corresponds to the LDP shortcut next-hop and has an owner of
LDP. The other route 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.
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.
When an IPv4 packet is received on an ingress network interface, a subscriber IES interface, or a
regular IES interface, the lookup of the packet by the ingress IOM will result in the packet being sent
labeled with the label stack corresponding to the NHLFE of the LDP LSP when the preferred RTM
entry corresponds to an LDP shortcut.
If the preferred RTM entry corresponds to an IP next-hop, the IPv4 packet is forwarded unlabelled.
When ECMP is enabled and multiple equal-cost next-hops exit for the IGP route, the ingress IOM
will spray the packets for this route based on hashing routine currently supported for IPv4 packets.
When the preferred RTM entry corresponds to an LDP shortcut route, spraying will be performed
across the multiple next-hops for the LDP FEC. The FEC next-hops can either be direct link LDP
neighbors or T-LDP neighbors reachable over RSVP LSPs in the case of LDP-over-RSVP but not
both.
When the preferred RTM entry corresponds to a regular IP route, spraying will be performed across
regular IP next-hops for the prefix..
The no form of this command disables the resolution of IGP routes using LDP shortcuts.
Default
no ldp-shortcut
ldp-sync-timer
Syntax ldp-sync-timer seconds
no ldp-sync-timer
Context config>router>interface
Description This command enables synchronization of IGP and LDP. When a link is restored after a failure, IGP
sets the link cost to infinity and advertises it. The actual value advertised in OSPF is 0xFFFF (65535).
The actual value advertised in IS-IS regular metric is 0x3F (63) and in IS-IS wide-metric is
0xFFFFFE (16777214). This feature is not supported on RIP interfaces.
Note that if an interface belongs to both IS-IS and OSPF, a physical failure will cause both IGPs to
advertise infinite metric and to follow the IGP-LDP synchronization procedures. If only one IGP
bounced on this interface or on the system, then only the affected IGP advertises the infinite metric
and follow the IGP-LDP synchronization procedures.
Next LDP hello adjacency is brought up with the neighbour. The LDP synchronization timer is started
by IGP from the time the LDP session to the neighbor is UP over the interface. This is to allow time
for the label-FEC bindings to be exchanged.
7450 ESS Router Configuration Guide
IP Router Configuration
Page 173