Link Ldp; Figure 48: Ldp Adjacency And Session Over Unnumbered Interface - Alcatel-Lucent 7450 Manual

Operation of LDP over an Unnumbered IP Interface

Figure 48: LDP Adjacency and Session over Unnumbered Interface

LSR A and LSR B have the following LDP identifiers respectively:
<LSR Id=A> : <label space id=0>
<LSR Id=B> : <label space id=0>
There are two P2P unnumbered interfaces between LSR A and LSR B. These interfaces are
identified on each system with their unique local link identifier. In other words, the combination of
{Router-ID, Local Link Identifier} uniquely identifies the interface in OSPF or IS-IS throughout
the network.
A borrowed IP address is also assigned to the interface to be used as the source address of IP
packets which need to be originated from the interface. The borrowed IP address defaults to the
system loopback interface address, A and B respectively in this setup. The user can change the
borrowed IP interface to any configured IP interface, loopback or not, by applying the following
command:
configure> router>interface>unnumbered [<ip-int-name| ip-address>]
When the unnumbered interface is added into LDP, it will have the following behavior.

Link LDP

Hello adjacency will be brought up using link Hello packet with source IP address set to the
interface borrowed IP address and a destination IP address set to 224.0.0.2.
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LSR-A:0
I/F 1
I/F 2
LSR-B:0
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7450 ESS MPLS Guide