MPLS Guide MPLS and RSVP-TE
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For LSPs configured with a primary path and a secondary or standby path and a
failure action of failover-or-down, the following points apply.
• The path is held in an operationally down state when its S-BFD session is down.
• If all paths are operationally down, the SR-TE LSP is taken operationally down
and a trap is generated.
• If S-BFD is enabled at the LSP or active path level, a switchover from the active
path to an available path is triggered if the S-BFD session fails on the active path
(primary or standby).
• If S-BFD is not enabled on the active path and this path is shut down, a
switchover is triggered.
• If S-BFD is enabled on the candidate standby or secondary path, this path is only
selected if S-BFD is up.
• An inactive standby path configured with S-BFD is only available to become
active if it is not operationally down; that is, its S-BFD session is up and all other
criteria for it to become operational are true. The path is held in an inactive state
if the S-BFD session is down.
• The system does not revert to the primary path or start a reversion timer when
the primary path is either administratively down or operationally down, because
the S-BFD session is not up or down for any other reason.
For LSPs configured with only one path and a failure action of failover-or-down, the
following points apply.
• The path is held in an operationally down state when its S-BFD session is down.
• If the path is operationally down, the LSP is taken operationally down and a trap
is generated.
For LSPs configured with one or more paths but no configured failure action, a BFD
trap is raised when the LSP goes down. The path state does not change.
3.12.6.2.1 SR-TE LSP State Changes and Failure Actions Based on S-BFD
When a path is first configured with S-BFD, it is held operationally down until BFD
comes up (subject to the BFD wait time).
Note: S-BFD and other OAM packets can still be sent on an operationally down SR-TE LSP.
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