Figure 43 BFD packet format
Vers: Protocol version. The protocol version is 1.
Diag: This bit indicates the reason for the last transition of the local session from up to some other
lists the states.
Table 19 Diag bit values
State (Sta): Current BFD session state. Its value can be 0 for AdminDown, 1 for Down, 2 for Init,
and 3 for Up.
Poll (P): If set, the transmitting system is requesting verification of connectivity, or of a parameter
change. If clear, the transmitting system is not requesting verification.
Final (F): If set, the transmitting system is responding to a received BFD control packet that had the
Poll (P) bit set. If clear, the transmitting system is not responding to a Poll.
Control Plane Independent (C): If set, the transmitting system's BFD implementation does not share
fate with its control plane (BFD is implemented in the forwarding plane and can continue to function
through disruptions in the control plane.) If clear, the transmitting system's BFD implementation
shares fate with its control plane.
Authentication Present (A): If set, the Authentication Section is present, and the session is to be
Demand (D): If set, Demand mode is active in the transmitting system (the system wishes to operate
in Demand mode, knows that the session is up in both directions, and is directing the remote system
Control Detection Time Expired
Echo Function Failed
Neighbor Signaled Session Down
Forwarding Plane Reset
Concatenated Path Down
Reverse Concatenated Path Down
Reserved for future use