Bidirectional Forwarding Detection (BFD) enabled BGP graceful restart
If you configure a BFD enabled BGP neighbor as a static BFD neighbor using the router bfd command, FGCP supports graceful restart of BFD enabled BGP. The router bfd command is needed as the BGP auto- start timer is 5 seconds. After HA failover, BGP on the new primary unit has to wait for 5 seconds to connect to its neighbors, and then register BFD requests after establishing the connections. With static BFD neighbors, BFD requests and sessions can be created as soon as possible after the failover. The new command get router info bfd requests shows the BFD peer requests.
A BFD session created for a static BFD neighbor/peer request will initialize its state as “INIT” instead of “DOWN” and its detection time asbfd-required-min-rx * bfd-detect-mult milliseconds.
When a BFD control packet with nonzero your_discr is received, if no session can be found to match the your_ discr, instead of discarding the packet, other fields in the packet, such as addressing information, are used to choose one session that was just initialized, with zero as its remote discriminator.
When a BFD session in the up state receives a control packet with zero as your_discr and down as the state, the session will change its state into down but will not notify this down event to BGP and/or other registered clients.