172 | Bidirectional Forwarding Detectionw w w . d e l l . c o m | s u p p o r t . d e l l . c o mTwo 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 controlpackets. Each system has its own transmit interval, which is the greater of the last received remoteDesired 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 controlpacket, after which the system determines that the session has failed. Each system has its owndetection time.• In Asynchronous mode: Detection time is the remote Detection Multiplier multiplied by greater ofthe 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 thelocal Desired Min TX and the remote Required Min RX Interval.Table 9-1. BFD Packet FieldsField DescriptionDiagnostic Code The reason that the last session failed.State The current local session state. See BFD sessions.Flag A bit that indicates packet function. If the poll bit is set, the receiving system must respond assoon as possible, without regard to its transmit interval. The responding system clears the pollbit and sets the final bit in its response. The poll and final bits are used during the handshakeand Demand mode (see BFD sessions).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. Discriminatorvalues are necessary to identify the session to which a control packet belongs since there canbe 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 remotesystem.Required Min RX Interval The minimum rate at which the local system would like to receive control packets from theremote 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 TypeAn optional method for authenticating control packets.Note: FTOS does not currently support the BFD authentication function.Authentication LengthAuthentication Data
