Reference Guide

100 | Bidirectional Forwarding Detection (BFD)
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4. The passive system receives the control packet, changes its state to Up. Both systems agree that a
session has been established. However, since 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 7-2. BFD Three-way Handshake
Session state changes
The following illustration shows how the session state on a system changes based on the status notification
it receives from the remote system. For example, if a session on a system is down, and it receives a Down
status notification from the remote system, the session state on the local system changes to Init.
4 Routers
6 Routers
8 Routers