Bfd Packet Format - 3Com S7906E Configuration Manual

At present, only the asynchronous mode is supported.
When a BFD session operates in Echo mode, the session is independent of the operating mode.
When the connectivity to another system needs to be verified explicitly, a system sends several
BFD control packets that have the Poll (P) bit set at the negotiated transmit interval. If no response
is received within the detection interval, the session is considered down. If the connectivity is found
to be up, no more BFD control packets are sent until the next command is issued.
Dynamic BFD parameter changes
After a BFD session is established, both ends can negotiate the related BFD parameters, such as the
minimum transmit interval, minimum receive interval, initialization mode, and packet authentication
mode. After that, both ends use the negotiated parameters, without affecting the current session state.

BFD Packet Format

Figure 1-3 illustrates the BFD control packet format. BFD control packets are encapsulated into UDP
packets with port number 3784.
Figure 1-3 BFD control packet format
Vers: Protocol version. The protocol version is 1.
Diag: This bit indicates the reason for the last transition of the local protocol from up to some other
state. Table 1-1
Table 1-1 Diag bit values
0
1
2
3
4
5
6
lists the states.
Diag Description
No Diagnostic
Control Detection Time Expired
Echo Function Failed
Neighbor Signaled Session Down
Forwarding Plane Reset
Path Down
Concatenated Path Down
1-4