Stewart, I wanted to follow up on the question you asked following the presentation in SPRING on Monday on draft-hegde-spring-node-protection-for-sr-te-paths.
After thinking about your question more, I think I understand it better. If I understand your question, I think you are concerned that with the proposed solution, a transit router acting as a PLR would need to maintain state for each SR-TE path that passes through the PLR. The presentation doesn't make this clear, but the draft itself goes into more detail explaining what state is needed. The short answer is that the PLR doesn't need per-path state. The long answer is below. For just link protection, the PLR needs a backup forwarding entry for every valid incoming first label that the PLR might receive. For link protection, this corresponds to needing a backup forwarding entry for every prefix-SID in the network and every adj-SID label advertised by the PLR. To provide protection against potential node failure, the PLR needs additional backup forwarding entries for a subset of valid incoming (first-label, second-label) pairs. Backup forwarding entries for label pairs are needed where the first-label is an adj-SID label advertised by the PLR or the first-label corresponds to a node-SID which is a direct neighbor of the PLR, and the second-label is a valid prefix-SID or adj-SID at that direct neighbor. These node-protecting backup forwarding entries can be created based on segment routing advertisements, independent of whatever SR-TE LSPs that have actually been instantiated in the network. Hopefully this answers the question. And hopefully that was actually your question in the first place. Thanks, Chris
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