Reference Guide

Field Description
NOTE: FTOS does not currently support multi-point sessions, Demand mode,
authentication, or control plane independence; these bits are always clear.
Detection Multiplier The number of packets that must be missed in order to declare a session down.
Length The entire length of the BFD packet.
My Discriminator A random number generated by the local system to identify the session.
Your Discriminator A random number generated by the remote system to identify the session. Discriminator values
are necessary to identify the session to which a control packet belongs because there can be
many sessions running on a single interface.
Desired Min TX
Interval
The minimum rate at which the local system would like to send control packets to the remote
system.
Required Min RX
Interval
The minimum rate at which the local system would like to receive control packets from the
remote system.
Required Min Echo
RX
The minimum rate at which the local system would like to receive echo packets.
NOTE: FTOS does not currently support the echo function.
Authentication Type,
Authentication
Length,
Authentication Data
An optional method for authenticating control packets.
NOTE: FTOS does not currently support the BFD authentication function.
Two important parameters are calculated using the values contained in the control packet.
Transmit interval Transmit interval is the agreed-upon rate at which a system sends control packets. Each
system has its own transmit interval, which is the greater of the last received remote Desired
TX Interval and the local Required Min RX Interval.
Detection time Detection time is the amount of time that a system does not receive a control packet, after
which the system determines that the session has failed. Each system has its own detection
time.
• In Asynchronous mode: Detection time is the remote Detection Multiplier multiplied by
greater of the remote Desired TX Interval and the local Required Min RX Interval.
• In Demand mode: Detection time is the local Detection Multiplier multiplied by the
greater of the local Desired Min TX and the remote Required Min RX Interval.
BFD Sessions
BFD must be enabled on both sides of a link in order to establish a session.
The two participating systems can assume either of two roles:
Active The active system initiates the BFD session. Both systems can be active for the same session.
Passive The passive system does not initiate a session. It only responds to a request for session
initialization from the active system.
A BFD session has two modes:
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