Reliable liveness detection is essential for SR policies to ensure fast and at the same time, deterministic protection switching without relying solely on IGP convergence. We verified that Seamless Bidirectional Forwarding Detection (S-BFD) can detect data-plane failures and trigger a fast SR policy switchover to a backup path in a multi-vendor SR-MPLS environment. For each initiator/reflector vendor pair listed in the table below, we established an SR policy between the Initiator and Reflector with a primary (protected) path via Spine 2 and a backup path via Spine 1. We started bidirectional service traffic and verified that packets followed the primary SR path while S-BFD sessions were UP. To emulate a data-plane failure without changing the IS-IS IGP, we selectively dropped the S-BFD control packets on Spine 2 toward the Reflector, while keeping the physical links up. After the S-BFD timeout, the sender switched to the backup path, and traffic went through it. We used an S-BFD timer of 3 × 50 ms, and for all tested pairs, the switchover occurred within the expected detection window. We confirmed the change by observing label stacks and traffic counters on the traffic generator.