Bidirectional Forwarding Detection (BFD) is a detection protocol that provides fast-forwarding, path-failure detection for
all media types, encapsulations, topologies, and routing protocols. The BFD Support for EIGRP IPv6 feature enables BFD to
interact with the Enhanced Interior Gateway Routing Protocol (EIGRP) to create BFDv6 sessions between EIGRP neighbors. In
a BFD-enabled EIGRP IPv6 session, BFD constantly monitors the forwarding path (from a local device to a neighboring device)
and provides consistent failure detection at a uniform rate. Because failure detection happens at a uniform rate and not at
variable rates, network profiling and planning is easier, and the reconvergence time remains consistent and predictable.
BFD is implemented in EIGRP at multiple levels; it can be implemented per interface or on all interfaces. When BFD is enabled
on a specific interface, all peer relationships formed through the EIGRP “Hello” mechanism on that interface are registered
with the BFD process. Subsequently, BFD establishes a session with each of the peers in the EIGRP topology and notifies EIGRP
through a callback mechanism of any change in the state of any peer. When a peer is lost, BFD sends a “peer down” notification
to EIGRP, and EIGRP unregisters a peer from BFD. BFD does not send a “peer up” notification to EIGRP when the peer is up because
BFD now has no knowledge of the state of the peer. This behavior prevents rapid neighbor bouncing and repetitive route computations.
The EIGRP “Hello” mechanism will later allow peer rediscovery and reregistration with the BFD process.