TI-LFA with Flex-Algo over SR MPLS

The specification of TI-LFA ensures that the Node-SIDs associated with a certain Flexible Algorithm (Flex-Algo) will be safeguarded by loop-free alternates, allowing an almost rapid convergence when a link or node fails. In addition, it demands that these "repairs" computed by those standards should only consider Node-SIDs or Adjacency-SIDs related to that FlexAlgo.
In this test, we performed the TI-LFA test within a network that runs FlexAlgo 128 (which prioritized paths with lower latency). After a link failure was detected on the primary path, automated traffic switching occurred quite rapidly to the alternate route under the strict definitions of Flex-Algo 128. It didn't default to a standard IGP alternative in its path decision. Our measured failover times stayed pretty much always under the threshold of 50 ms, fully aligned with our sub-50 ms target for high-available services.

This test has generally confirmed the applicability of TI-LFA in protecting SR-MPLS networks under FlexAlgo constraints in fast reroute settings and for adaptation to link failures. With small changes—like merging routing capability into IGP advertisements, multi-vendor inter-operability can be ensured even in advanced SR deployments.