Bfd Packet Format - HPE FlexNetwork HSR6800 series Configuration Manual

•
Active mode—BFD actively sends BFD control packets regardless of whether any BFD control
packet is received from the peer.
•
Passive mode—BFD does not send control packets until a BFD control packet is received from
the peer.
At least one end must operate in active mode for a BFD session to be established.
After a BFD session is established, both ends must operate in one of the following BFD operating
modes:
•
Asynchronous mode—Both endpoints periodically send BFD control packets to each other.
BFD considers that the session is down if it receives no BFD control packets within a specific
interval.
•
Demand mode—No BFD control packets are exchanged after the session is established. It is
assumed that the endpoints have another way to verify connectivity to each other. However,
either host might still send BFD control packets if needed.
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 connectivity is found to be
up, no more BFD control packets are sent until the next command is issued.
NOTE:
• Only the asynchronous mode is supported.
• When a BFD session is maintained by sending Echo packets, the session is independent of the
operating mode.
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

BFD control packets are encapsulated into UDP packets with port number 3784 for single-hop
detection or port number 4784 for multi-hop detection (also can be 3784 based on the configuration
task). BFD echo packets have a similar format as BFD control packets with UDP port number 3785
except that the Desired Min TX Interval and Required Min RX Interval fields are null.
illustrates the packet format.
Figure 54 BFD packet format
•
Vers—Protocol version. The protocol version is 1.
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Figure 54