Deployment Guide
NOTE: The Dell Networking operating system 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 noties 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 noties 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.
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 8. BFD in IPv4 Packet Format
Field
Description
Diagnostic Code The reason that the last session failed.
138 Bidirectional Forwarding Detection (BFD)