When a path is first configured with S-BFD, it is held operationally down until BFD comes up (subject to the BFD wait time).
The BFD wait-for-up-timer is started when BFD is first enabled on a path or when an existing S-BFD session transitions from up to down. If this timer expires before S-BFD is up, the path is torn down and the LSP retry timer is started.
In the S-BFD up-to-down case, if there is only one path, the LSP is torn down when S-BFD fails and then deprogrammed when the wait-for-up-timer expires.
If all the paths of an LSP are operationally down due to S-BFD, the LSP is taken operationally down and the BFD wait-for-up-timer is started for each path. If one or more paths do not have S-BFD configured or are otherwise not down, the LSP is not taken operationally down.
When an existing S-BFD session fails on a path and the failure action is failover-or-down, the configured failure action is activated, the path is put into the operationally down state, and a trap is raised. The state and reason code are displayed with the show>router>bfd>seamless-bfd command.