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How BFD Works

In a BFD-configured network, when a client launches a BFD session with a peer, BFD begins sending slow, periodic BFD control packets that contain the interval values that you specified when you configured the BFD peers. This is known as the initialization state and BFD does not generate any up or down notifications in this state.

When another BFD interface acknowledges the BFD control packets, the session moves into an up state and begins to more rapidly send periodic control packets.

If a data path failure occurs and BFD does not receive a control packet within the configured amount of time, the data path is declared down and BFD notifies the BFD client. The BFD client can then perform the necessary actions to reroute traffic. This process can be different for different BFD clients. All BFD-configured IGP clients (like IS-IS, OSPF, PIM, and RIP) launch BFD sessions when they detect neighbors through their own hello protocols. However, a static BFD client launches a BFD session when it detects that its next hop is resolved.

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