Vyatta NOS documentation

Learn how to install, configure, and operate Vyatta Network Operating System (Vyatta NOS), which helps to drive our virtual networking and physical platforms portfolio.

Format of a BFD control packet

A BFD control packet is sent in an encapsulation and the packet has a mandatory section and an optional authentication section. The format of the authentication section, if present, depends on the type of authentication in use.

Figure 1. Format of a BFD control packet
Format of BFD Control Packet
The preceding figure displays a cross-sectional view of the BFD control packet. The packet dividers are described here:
  • Vers (Version)—Version of the BFD protocol.
  • Diag (Diagnostics)—Diagnostic code that indicates the reason for the last change of the local system in a BFD session state.
  • Sta (State)—State of the current BFD session as seen by the transmitting system.
  • P (Poll)—Indication that the transmitting system is requesting verification of connectivity or a parameter change, and is expecting a packet with the Final (F) bit in reply. If not set, the transmitting system is not requesting verification.
  • F (Final)—Indication that the transmitting system is responding to a received BFD control packet that has the Poll (P) bit set. If not set, the transmitting system is not responding to a Poll.
  • C (Control Plane Independent)—Indication that the implementation of the BFD session of the transmitting system is independent of the control plane. If not set, the implementation of the BFD session of the transmitting system depends on the control plane.
  • A (Authentication Present)—Indication that the session is to be authenticated. If not set, the session is not authenticated.
  • D ( Demand)—Indication that the demand mode is active in the transmitting system. In demand mode, the system recognizes that the session is active in both directions, and directs the remote system to halt the periodic transmission of BFD control packets. If not set, demand mode is not active in the transmitting system.
  • M ( Multipoint)—Indication that the bit is reserved for future point-to-multipoint extensions to BFD. It must be zero on both transmit and receipt.
  • Detect Mult—Detection time multiplier. The negotiated transmission interval, multiplied by this value, provides the detection time for the receiving system in asynchronous mode.
  • Length—Length of the BFD control packet, in bytes.
  • My Discriminator—Unique, nonzero discriminator that is generated by the transmitting system, used to demultiplex multiple BFD sessions between the same pair of systems.
  • Your Discriminator—Discriminator received from the corresponding remote system. This field reflects the received value of My Discriminator, or is zero if that value is unknown.
  • Desired Min TX Interval—Minimum interval, in microseconds, that the local system prefers to use when transmitting BFD control packets.
  • Required Min RX Interval—Minimum interval, in microseconds, between received BFD control packets that the system is capable of supporting.
  • Required Min Echo RX Interval—Minimum interval, in microseconds, between received BFD echo packets that the system is capable of supporting.

  • Auth Type—Authentication type in use, if the Authentication Present (A) bit is set.
  • Auth Len—Length, in bytes, of the authentication section, including the Auth Type and Auth Len fields.
  • Authentication Data—Information used to authenticate the BFD sessions.