BFD for BGP Session Creation and Deletion

The parameters for session creation are applied according to a specific hierarchy. When sessions are deleted, their states change according to the reason they were deleted.

For multihop BGP neighbors, session parameter values are applied according to the following hierarchy:

Values configured at the neighbor level
Values configured at the BGP neighbor group level
Values configured at the global BGP level
Default values

For single-hop neighbors, interface-level BFD parameters are applied.

BFD for BGP sessions are deleted in the following scenarios.

Session moves from Established to another state. BFD sessions are deleted for a source or destination IPv4 or IPv6 address when a BGP session moves from the Established state to another BGP state.
A neighbor is unconfigured locally. BFD sessions are deleted when a BGP session for a neighbor is unconfigured locally. If this unconfigured session is in an Established state and running a BFD session with a neighbor that is up, BGP sends a Cease message to the peer and deletes the BFD session. Upon receiving this Cease message, the neighbor deletes the BFD session and moves to an Idle state.