Label Distribution Protocol
394
MPLS Guide
© 2022 Nokia.
Use subject to Terms available at: www.nokia.com
3HE 18686 AAAB TQZZA
5.1.15.1 Feature Behavior
The following describes the behavior of this feature.
• When LDP resolves a primary next hop in the RTM or a remote LFA or TI-LFA
backup next hop using an SR tunnel in the TTM, LDP programs a primary LDP
NHLFE and a backup LDP NHLFE with an implicit null label value pointing to the
SR tunnel that has the remote LFA or TI-LFA backup programmed for the same
prefix.
• If the LDP FEC primary next hop fails and LDP has preprogrammed a remote
LFA and TI-LFA next hop with an LDP backup NHLFE pointing to an SR tunnel,
the LDP ILM/LTN switches to it.
• If the LDP FEC primary next hop becomes unresolved in the RTM, LDP switches
the resolution to an SR tunnel in the TTM, if one exists, following the steps
described in Stitching in the LDP-to-SR Direction.
• If both the LDP primary next hop and a regular LFA next hop become resolved
in RTM, the LDP FEC programs the primary NHLFE and backup NHLFE.
5.1.16 TCP MD5 Authentication
The operation of a network can be compromised if an unauthorized system is able to
form or hijack an LDP session and inject control packets by falsely representing itself
as a valid neighbor. This risk can be mitigated by enabling TCP MD5 authentication
on one or more of the sessions.
Note: The LDP packet is not sent over the SR tunnel. The LDP label is stitched to the
segment routing label stack. LDP points both the LDP ILM and the LTN to the backup LDP
NHLFE, which uses the SR tunnel endpoint.
Note: If the LDP FEC primary next hop failure impacts only the LDP tunnel primary next hop
but not the SR tunnel primary next hop, the LDP backup NHLFE points to the primary next
hop of the SR tunnel; the LDP ILM/LTN traffic follows this path instead of the remote LFA or
TI-LFA next hop of the SR tunnel until the remote LFA or TI-LFA next hop is activated.
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