Reference Guide

Bidirectional Forwarding Detection (BFD) | 149

Bidirectional Forwarding Detection (BFD)

Bidirectional Forwarding Detection (BFD) is supported only on the S5000 switch.

This chapter contains the following major sections:

• Protocol Overview

• How BFD Works

• Configuring Bidirectional Forwarding Detection

• Configuring BFD for OSPF

• Configuring BFD for IS-IS

• Configuring BFD for BGP

• Configuring Protocol Liveness

• Troubleshooting BFD

Protocol Overview

Bidirectional Forwarding Detection (BFD) is a protocol that is used to rapidly detect communication

failures between two adjacent systems. It is a simple and lightweight replacement for existing routing

protocol link state detection mechanisms. It also provides a failure detection solution for links on which no

routing protocol is used.

BFD is a simple hello mechanism. Two neighboring systems running BFD establish a session using a

three-way handshake. After the session has been established, the systems exchange periodic control

packets at sub-second intervals. If a system does not receive a hello packet within a specified amount of

time, routing protocols are notified that the forwarding path is down.

BFD provides forwarding path failure detection times on the order of milliseconds rather than seconds as

with conventional routing protocol hellos. It is independent of routing protocols, and as such provides a

consistent method of failure detection when used across a network. Networks converge faster because BFD

triggers link state changes in the routing protocol sooner and more consistently, because BFD can

eliminate the use of multiple protocol-dependent timers and methods.

BFD also carries less overhead than routing protocol hello mechanisms. Control packets can be

encapsulated in any form that is convenient, and, on Dell Networking routers, sessions are maintained by

BFD Agents. Only session state changes are reported to the BFD Manager, which in turn notifies the

routing protocols that are registered with it.