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.

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

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.