Overview of BFD

Definition

Bidirectional Forwarding Detection (BFD) is a fault detection protocol that can quickly detect a communication failure between devices and notify upper-layer applications.

Purpose

To minimize the impact of device faults on services and improve network reliability, a network device must be able to quickly detect faults when communicating with adjacent devices. Measures can then be taken to promptly rectify the faults to implement service continuity.

On a live network, link faults can be detected using either of the following mechanisms:

Hardware detection: For example, the Synchronous Digital Hierarchy (SDH) alarm function can be used to quickly detect link hardware faults.
Hello detection: If hardware detection is unavailable, Hello detection can be used to detect link faults.

However, the two mechanisms have the following issues:

Only certain media support hardware detection.
Hello detection takes more than 1 second to detect faults. When traffic is transmitted at gigabit rates, such slow detection causes great packet loss.
On a Layer 3 network, the Hello packet detection mechanism cannot detect faults for all routes, such as static routes.

BFD resolves these issues by providing:

A low-overhead, short-duration method is used to detect faults in a path between adjacent forwarding engines. The faults can be interface, data link, and even forwarding engine faults.
A single, unified mechanism is used to monitor any media and protocol layers in real time.

Benefits

BFD offers the following benefits:

BFD rapidly monitors link and IP route connectivity to improve network performance.
Adjacent systems running BFD rapidly detect communication failures and establish a backup channel to restore communications, which improves network reliability.