The TI-LFA repair tunnel can have a maximum of three additional labels pushed in addition to the label of the destination node or prefix. The user can set a lower maximum value for the additional FRR labels by configuring the ti-lfa max-sr-frr-labels labels CLI option. The default value is 2.
The datapath models the backup path like a SR-TE LSP and therefore uses a super-NHLFE pointing to the NHLFE of the first hop in the repair tunnel. That first hop corresponds to either an adjacency SID or a node SID of the P node.
There is the special case where the P node is adjacent to the node computing the TI-LFA backup, and the Q node is the same as the P node or adjacent to the P node. In this case, the datapath at the computing router pushes either zero labels or one label for the adjacency SID between P and Q nodes. The backup path uses a regular NHLFE in this case like in base LFA or remote LFA features. Figure: Selecting link-protect TI-LFA backup path shows and example of a single label in the backup NHLFE.