Dell Force10 E600i FTOS Version 8.4.1.5 Configuration Guide for ExaScale - Page 166
How BFD Works, BFD packet format
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www.dell.com | support.dell.com How BFD Works Two neighboring systems running BFD establish a session using a three-way handshake. After the session has been established, the systems exchange control packets at agreed upon intervals. In addition, systems send a control packet anytime there is a state change or change in a session parameter; these control packets are sent without regard to transmit and receive intervals. Note: FTOS 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. BFD packet format Control packets are encapsulated in UDP packets. Figure 11-1 shows the complete encapsulation of a BFD control packet inside an IPv4 packet. 166 | Bidirectional Forwarding Detection
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