When Flexible Algorithms are used to create constraint-based topologies, fast reroute must operate consistently within the selected algorithm without falling back to unintended paths. We verified TI-LFA operation within an IS-IS Segment Routing MPLS Flexible Algorithm 128 (delay-based) topology by rotating the Device Under Test (DUT) across the vendor routers listed in the Table below while keeping the remaining nodes fixed. We connected the traffic source behind the DUT and the traffic sink behind node HPE ACX7100-48L, and verified that the DUT steered traffic toward node HPE ACX7100-48L according to the Flex-Algo 128 delay shortest path. We set the delay so that the direct DUT to egress PE direction was preferred and the alternative path via node Arista 7280R3 had a higher delay, then confirmed that forwarding entries matched the expected Flex-Algo 128 preference. We disabled the laser on the link between the DUT and the egress PE to trigger TI-LFA and observed that the DUT acted as the local repair, switching traffic within the expected TI-LFA protection time (<50 ms) to another loop-free precomputed path over the remaining Flex-Algo 128 topology via the node Arista 7280R3. To validate algorithm separation, we then disabled the DUT to the Arista 7280R3 link and confirmed that traffic dropped rather than switching to the remaining path via node Raisecom RAX721-T-4C24, which was part of the default Algorithm 0 metric tuning but not part of the Flex-Algo 128 delay topology.