LDP will advertise/withdraw unnumbered interfaces using the Address/Address-Withdraw message. The borrowed IP address of the interface is used.
A FEC can be resolved to an unnumbered interface in the same way as it is resolved to a numbered interface. The outgoing interface and next-hop are looked up in the RTM cache. The next-hop consists of the router-id and link identifier of the interface at the peer LSR.
LDP FEC ECMP next-hops over a mix of unnumbered and numbered interfaces is supported.
All LDP FEC types are supported.
The fec-originate command is supported when the next-hop is over an unnumbered interface.
All LDP features are supported except for the following:
BFD cannot be enabled on an unnumbered LDP interface. This is a consequence of the fact that BFD is not supported on unnumbered IP interface on the system.
As a consequence of item 1, LDP FRR procedures will not be triggered via a BFD session timeout but only by physical failures and local interface down events.
Unnumbered IP interfaces cannot be added into LDP global and peer prefix policies.