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Routing & Switching · Intermediate

Bidirectional Forwarding Detection (BFD)

A lightweight hello protocol that detects forwarding path failures in milliseconds and notifies routing protocols.

Definition

BFD runs independently of routing protocols, sending control packets at intervals as low as tens of milliseconds, often in hardware. OSPF, EIGRP, IS-IS, BGP, HSRP and static routes can register as BFD clients and tear down adjacencies immediately when BFD declares a session down. Echo mode sends packets the neighbor loops back through its forwarding plane.

Example

bfd interval 50 min_rx 50 multiplier 3 ; ip ospf bfd

Exam tip

BFD detection time is interval multiplied by the multiplier; 50 ms x 3 = 150 ms.

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