1-4
BFD Packet Format
As illustrated in
Figure 1-3
, BFD control packets use UDP and port number 3784.
Figure 1-3
BFD control packet format
z
Vers: Protocol version. The protocol version is 1.
z
Diag: This bit indicates the reason for the last transition of the local protocol from
up
to some other
state.
Table 1-1
lists the states.
Table 1-1
Diag bit values
Diag
Description
0 No
Diagnostic
1
Control Detection Time Expired
2
Echo Function Failed
3
Neighbor Signaled Session Down
4
Forwarding Pane Reset
5 Path
Down
6
Concatenated Path Down
7 Administratively
Down
8~31
Reserved for future use
z
State (Sta): Current BFD session state. Its value can be 0 for AdminDown, 1 for Down, 2 for Init,
and 3 for Up.
z
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 to cease the periodic transmission of BFD Control packets). If clear, Demand mode
is not active in the transmitting system.
z
Poll (P): If set, the transmitting system is requesting verification of connectivity, or of a parameter
change, and is expecting a packet with the Final (F) bit in reply. If clear, the transmitting system is
not requesting verification.
z
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.
z
Control Plane Independent(C): If set, the transmitting system's BFD implementation does not share
fate with its control plane (in other words, BFD is implemented in the forwarding plane and can
