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MPLS Guide
FEC resolution:
All LDP features supported for numbered IP interfaces are supported for
unnumbered interfaces, with the following exceptions:
The unnumbered interface feature also extends the support of LSP ping and LSP
traceroute to test an LDP unicast FEC that is resolved over an unnumbered LDP
interface.
5.1.13 LDP Fast Reroute (FRR)
LDP Fast Reroute (FRR) provides local protection for an LDP FEC by precalculating
and downloading a primary and a backup NHLFE for the FEC to the LDP FIB. The
primary NHLFE corresponds to the label of the FEC received from the primary next
hop as per the standard LDP resolution of the FEC prefix in the RTM. The backup
NHLFE corresponds to the label received for the same FEC from a Loop-Free
Alternate (LFA) next hop.
LDP FRR protects against single link or single node failure. SRLG failure protection
is not supported.
3HE 18686 AAAB TQZZA
• LDP advertises/withdraws 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 is 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
are supported.
• All LDP FEC types are supported.
• The fec-originate command is supported when the next hop is over an
unnumbered interface.
• BFD is not supported on unnumbered IP interfaces
• LDP FRR is not triggered by a BFD session timeout, only by a physical failure or
the local interface going down
• unnumbered IP interfaces cannot be added into LDP global and peer prefix
policies
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