Understanding the backup path calculation
Figure 13.2 illustrates the TI-LFA Node+SRLG protection.
Figure 13.2 – TI-LFA Node + SRLG protection primary and backup paths
The following explanation details the computation and selection of the primary path and backup path.
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 categorized as TI-LFA (node+srlg) since both node protection and SRLG protection are explicitly requested in the P2 router configuration.
TI-LFA
The post-convergence path for this request would be P2 - P6 - P7 - P4 - PE5, with a cost of 220. In addressing the link failure on the P2–P3 link, TI-LFA provides Node+SRLG protection by collecting the following information:
- P-Space of P2 along the post-convergence path: The group of routers on the post-convergence path reachable from...
