Dell C9000 Series Networking Configuration Manual page 165

NOTE: The Dell Networking OS does not support multi-hop BFD sessions.
If a system does not receive a control packet within an agreed-upon amount of time, the BFD agent changes
the session state to Down. It then notifies the BFD manager of the change and sends a control packet to the
neighbor that indicates the state change (though it might not be received if the link or receiving interface is
faulty). The BFD manager notifies the routing protocols that are registered with it (clients) that the forwarding
path is down and a link state change is triggered in all protocols.
NOTE: A session state change from Up to Down is the only state change that triggers a link state change
in the routing protocol client.
Bidirectional Forwarding Detection (BFD) 165