Understanding the backup path calculation
The following topology diagram describes the backup path calculation:
Figure 11.2 – TI-LFA SRLG protection primary and backup paths
The detailed explanation of the computation and selection of the primary path and backup path for the preceding topology is as follows.
Primary path
The primary path from P2 to PE5 goes via P3, with the end-to-end path cost of 30 (P2 - P3 - P4 - PE5), making it the shortest path.
Backup path
The backup path is classified as TI-LFA (srlg) because SRLG protection is explicitly requested in the P2 router configuration:
TI-LFA
In addressing the link failure on the P2-P3 link, TI-LFA provides SRLG protection by collecting the following information:
The post-convergence path in the scenario, including the local srlg-disjoint request, would be P2 - P6 - P7 - P3 - P4 - PE5, with a cost of 140.
- P-Space of P2 along the post-convergence path: The group of...
