S-BFD for SR policies

S-BFD is supported on segment lists for both static SR policies and BGP SR policies by binding a maintenance policy containing an S-BFD configuration to an imported SR policy route or a static SR policy. S-BFD packets are encapsulated on the SR policy segment lists in the same way as for SR-TE LSP paths. As in the case of SR-TE LSPs, the discriminator of the local node as well as a mapping to the far-end reflector node discriminators is first required. BFD sets the remote discriminator at the initiator of the S-BFD session based on a lookup in the S-BFD reflector discriminator using the endpoint address of the SR policy candidate path. A candidate path of an SR policy is only treated as available if the number of up S-BFD sessions equals or exceeds a configurable threshold.

Note: When an SR policy candidate path is first programmed, a 3 second initialization hold timer is triggered. This allows the establishment of all the S-BFD sessions for all programmed paths before it decides which candidate path to activate among the eligible ones (eligible means number of segment lists with S-BFD sessions in up-state that is higher or equal to a configured threshold).

Because this is set to 3 seconds, it is recommended that the transmit and receive control packet timers are set to no more than 1 second with a maximum multiplier of 3 for S-BFD sessions.

S-BFD control packet timers, that are configurable down to 10ms, are supported for specific SR OS platforms with CPM network processor support.

The router supports an uncontrolled return path for S-BFD packets on SR policies. By default, the BFD reply packet from the reflector node is routed out-of-band to the head end of the SR policy.