Users 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 13. 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
Bidirectional Forwarding Detection (BFD) 173