Generic BFD session parameters are configured for VCCV using the bfd-template command, in the config>router>bfd context. However, there are some restrictions.
For VCCV, the BFD session cannot terminate on the CPM network processor. Therefore, an error is generated if the user tries to bind a BFD template using the type cpm-np command within the config>router>bfd>bfd-template context.
Attempting to bind a BFD template with any unsupported transmit or receive interval generates an error.
Finally, attempting to commit changes to a BFD template that is already bound to a PW where the new values are invalid for VCCV BFD results in an error.
If the preceding BFD timer values are changed in a specified template, any BFD sessions on PWs to which that template is bound try to renegotiate their timers to the new values.
Commands within the BFD-template use a begin-commit model. To edit any value within the BFD template, a begin command needs to be executed after the template context has been entered. However, a value is still stored temporarily in the template-module until the commit command is issued. When the commit is issued, values are used by other modules such as the MPLS-TP module and BFD module.
For PWs where the PW template does not apply, a named BFD template is configured on the spoke-SDP using the config service [epipe | cpipe | apipe | fpipe | ipipe] spoke-sdp bfd bfd-template command and then enabled using the config service [epipe | cpipe | apipe | fpipe | ipipe] spoke-sdp bfd bfd-enable command. For example, LDP-signaled spoke-SDPs for a VLL service that uses the PW ID FEC (FEC128) or spoke-SDPs with static PW labels.
Configuring and enabling a BFD template on a static PW already configured with MPLS-TP identifiers (that is, with a pw-path-id) or on a spoke-SDP with a configured pw-path-id is not supported. Likewise, if a BFD template is configured and enabled on a spoke-SDP, a pw-path-id cannot be configured on the spoke-SDP.
The bfd-enable command is blocked on a spoke-SDP configured with VC-switching. This is because VCCV BFD always operates end-to-end on an MS-pseudowire. It is not possible to extract VCCV BFD packets at the S-PE.
For IES and VPRN spoke-SDP termination where the PW template does not apply (that is, where the spoke-SDP is signaled with LDP and uses the PW ID FEC (FEC128)), the BFD template is configured using the config service ies | vprn if spoke-sdp bfd bfd-template command, then enabled using the config service ies | vprn if spoke-sdp bfd bfd-enable command.
For H-VPLS, where the PW template does not apply (that is, LDP-VPLS spoke SDPs that use the PW ID FEC(FEC128)) the BFD template is configured using the configure service vpls spoke-sdp bfd bfd-template or the configure service vpls mesh-sdp bfd bfd-template command. VCCV BFD is then enabled with the bfd-enable command under the vpls spoke-sdp bfd or vpls mesh-sdp bfd context.
PWs where the PW template does apply and that support VCCV BFD are as follows:
BGP-AD, which is signaled using the Generalized PW ID FEC (FEC129) with Attachment Individual Identifier (AII) type I
BGP VPLS
BGP VPWS
For these PW types, a named BFD template is configured and enabled from the PW template binding context.
For BGP VPWS, the BFD template is configured using the config service epipe bgp pw-template-binding bfd-template name command, then enabled using the config service epipe bgp pw-template-binding bfd-enable command.
The ability to determine PW forwarding state from VCCV BFD on the pseudowire is configured using the failure-action down command. It is possible to configure failure-action whether a spoke-SDP is administratively shutdown or not. It is therefore recommended to first configure VCCV BFD to ensure the spoke-SDP is forwarding, and then configure the failure-action command. If the failure-action down command is configured, the router continues to send VCCV BFD packets on a spoke-SDP or mesh-SDP that is operationally down because of the VCCV BFD session being in the down state. The router can then rapidly detect when connectivity is restored.
The wait-for-up-timer can be configured when failure-action down is configured. The wait-for-up-timer timer is triggered when a spoke-SDP or mesh-SDP is first administratively enabled and when a VCCV BFD session transitions from up to down. It is useful to allow time for BFD sessions to come up when the spoke-SDP is initially no shutdown. This provides the BFD session time to settle before it selects the active spoke-SDP for use in a redundant set. It also prevents excessive flapping of the operation state of a spoke-SDP if a VCCV BFD session is bouncing.