Topology Independent Loop Free Alternative over SR-MPLS

Topology Independent Loop-Free Alternate (TI-LFA) is a fast reroute mechanism for the Segment Routing (SR) MPLS networks, ensuring minimum service disruption by pre-installed backup forwarding entries for each protected destination. Our evaluation focuses on protecting local and remote SRLGs and micro-loop avoidance (MLA). The test case involved setting up four SR-capable nodes in a diamond topology running an L3VPN service to check TI-LFA's performance under different failure scenarios.
In the first step, we confirmed that pre-computed backup paths for TI-LFA immediately become active whenever the primary link fails, with failure times recorded between 3.9 and 42 milliseconds. We also assigned SRLG identifiers at both ends of the key links to verify that TI-LFA would reroute traffic correctly under local and remote SRLG conditions. RFC8333 micro-loop avoidance strategies, meanwhile, were tested, thus ensuring there is no transient looping during route convergence and steady data forwarding.

Simulating a primary path failure caused TI-LFA to switch traffic over to its backup path in milliseconds and revert back once the original link returned after going along with a newly calculated primary path. L3VPN traffic recorded no substantial interruption or packet loss throughout the test. The network handled shared-risk link failures, topological changes, and micro-loop conditions without compromising service quality. Overall, these results validate that TI-LFA is a reliable fast-reroute strategy for SR-MPLS environments that delivers very strong resilience and continuous service in very different operational conditions. Thus, it is important for service providers with critical SLAs in today's IP/MPLS infrastructures.