Configuring BFD BFD Overview
OmniSwitch AOS Release 8 Network Configuration Guide December 2017 page 20-13
Demultiplexing
Each BFD session must be able to uniquely identify itself and received BFD packets among the myriad of
BFD sessions that are running. Each BFD peer must choose an identifying and unique discriminator value.
This value is sent in the “My Discriminator” field of the BFD control packet, and is reflected back in the
“Your Discriminator” field of the control packet sent from the remote peer. Once the system has echoed
the respective “Your Discriminator” value back to its peer, the packets are demultiplexed (converted back
into their original separate signals).
BFD Timer Negotiation
The BFD control packet contains information about how quickly a system would like to send packets to its
peer, as well as how rapidly it is willing to receive packets from the peer. The BFD detection time is not
carried explicitly in the protocol, but rather, it is determined by the receiving system independently based
on the transmission interval (TX) and Detection Time Multiplier that have been negotiated.
The Detection Time Multiplier field value is approximately the number of packets that must be missed in
order to declare a session down. In Asynchronous mode, detection times can be different in each direction.
The local system detection time in this mode equals the value of Detection Time Multiplier received from
the remote system multiplied by the negotiated transmission interval (TX). Because the time values for
BFD control packet transmissions and session detection are being constantly negotiated by the
participating BFD peers, they can be changed at any time. They are also independent in each direction for
each session.
To change the rate at which BFD control packets are received, you can change the Required Min RX
Interval at any time to any value. This new value is sent in the next outgoing packet so that the remote
system can accommodate the changes made. Similarly, to change the rate at which BFD control packets
are transmitted, you can change the Desired Min TX Interval at any time to any value.
With some exceptions, a system cannot transmit control packets with an interval shorter than the larger
value of the TX interval and RX interval fields. This means that the system with the slower rate
determines the BFD control packet transmission speed.
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