Dell C9000 Series Networking Configuration Manual page 169

2 When the passive system receives any of these control packets, it changes its session state to Init and
sends a response that indicates its state change. The response includes its session ID in the My
Discriminator field and the session ID of the remote system in the Your Discriminator field.
3 The active system receives the response from the passive system and changes its session state to Up. It
then sends a control packet indicating this state change. This is the third and final part of the handshake.
Now the discriminator values have been exchanged and the transmit intervals have been negotiated.
4 The passive system receives the control packet and changes its state to Up. Both systems agree that a
session has been established. However, because both members must send a control packet — that
requires a response — anytime there is a state change or change in a session parameter, the passive
system sends a final response indicating the state change. After this, periodic control packets are
exchanged.
Figure 11. BFD Three-Way Handshake State Changes
Bidirectional Forwarding Detection (BFD) 169