When the PLR is the ingress LER node and the outgoing interface of the bypass LSP is unnumbered, the user must assign a borrowed IP address to the interface that is different from the system interface; otherwise, the bypass LSP will not come up.
In addition, the PLR node includes the IF_ID RSVP_HOP object (C-Type = 3) in the PATH message if the outgoing interface of the bypass LSP is unnumbered. If the outgoing interface of the bypass LSP is numbered, the PLR node includes the IPv4 RSVP_HOP object (C-Type = 1).
When the MP node receives the PATH message over the bypass LSP, it creates the merge-point context for the protected LSP and associates it with the existing state if any of the following is satisfied:
the C-Type value of the RSVP_HOP object has changed
the C-Type is the value for the IF_ID RSVP_HOP object (C-Type = 3) and it has not changed, but the IF_ID TLV is different
the IPv4 Next/Previous Hop Address field in the RSVP_HOP object has changed, regardless of the C-Type value
This behavior at the PLR and MP nodes is the same for both link protection and node protection FRR.
See RSVP-TE Support for Unnumbered Interfaces for information about unnumbered interfaces.