Administrator Guide

BFD Packet Format
Control packets are encapsulated in user datagram protocol (UDP) packets. The following illustration shows the complete encapsulation of
a BFD control packet inside an IPv4 packet.
Figure 9. BFD in IPv4 Packet Format
Field
Description
Diagnostic Code The reason that the last session failed.
State The current local session state. Refer to BFD Sessions.
Flag A bit that indicates packet function. If the poll bit is set, the receiving system must respond as soon as possible,
without regard to its transmit interval. The responding system clears the poll bit and sets the nal bit in its
response. The poll and nal bits are used during the handshake and in Demand mode (refer to BFD Sessions).
NOTE: Dell Networking OS does not currently support multi-point sessions, Demand mode,
authentication, or control plane independence; these bits are always clear.
Bidirectional Forwarding Detection (BFD) 145