The failure-action down command is supported for point-to-point RSVP (including mesh point-to-point and one-hop point-to-point auto-LSPs) and LDP LSPs. This command is configured within the config>router>mpls>lsp>bfd, config>router>mpls>lsp-template>bfd, or config>router>ldp>lsp-bfd contexts. For RSVP LSPs, it is only supported at the LSP level and not at the primary or secondary path levels. When configured, an LSP is made unavailable as a transport if BFD on the LSP goes down.
If BFD is disabled, MPLS installs the LSP as ‟usable” in the TTM. The failure-action configuration is ignored.
If BFD is enabled and no failure-action is configured, MPLS installs the LSP as ‟usable” in the TTM regardless of the BFD session state. BFD generates BFD Up and BFD Down traps.
If BFD is enabled and failure-action down is configured:
BFD traps are still generated when the BFD state machine transitions.
If the BFD session is up for the active path of the LSP, the LSP is installed as ‟usable” in the TTM. If the BFD session is down for the active path, the LSP is installed as ‟not-usable” in the TTM.
When an LSP is first activated using the no shutdown command, and its LSP BFD session first starts to come up, the LSP is installed as ‟not-usable” in the TTM to any user until the BFD session transitions to the up state, despite the FEC for the corresponding LSP being installed by the TTM. Users include all protocols, including those in RTM. A tunnel that is marked as down in the TTM is not available to RTM, and all routes using it are withdrawn. SDP auto-bind does not make use of an LSP until it is installed as ‟usable”.
If the BFD session is up on the active path and the LSP is installed as ‟usable” in the TTM, and if the LSP switches from its current active path to a new path, the system triggers a new BFD bootstrap using LSP ping for the new path, and waits for a maximum of 10 s for the BFD session to come up on the new path before switching traffic to it. If the BFD session does not come up on the new path after 10 s, the system switches to the new path anyway and install the LSP as ‟not-usable” in the TTM. This is the only scenario where a switch of the active path can be delayed because of the BFD transition state.
If the BFD session is down on the active path and the LSP was already installed as ‟not-usable” in the TTM, then the system immediately switches to the new path without waiting for BFD to become operationally up.
If BFD is disabled, MPLS installs the LSP as ‟usable” in the TTM. The failure-action configuration is ignored. LSP ping and LSP trace are still able to test an LSP when BFD is disabled.
BFD session state is never used to trigger a switch of the active path when failure-action down is configured.