Using Bidirectional Forwarding Detection (BFD) in Your Network

Bidirectional Forwarding Detection (BFD) provides a mechanism for detecting a communications failure with a forwarding plane next hop in less than one second, independent of media and protocol. With high speed data rates, a failure requiring several seconds to detect results in the loss of a large amount of data. BFD augments the Hello mechanism of various routing protocols that have failure detection times greater than a second. Because routing protocol Hello mechanisms do not tend have the same timing mechanics, BFD also provides a network administrator with a consistent means of reacting to next hop status changes regardless of the routing protocol. BFD shares its primary goal of providing the up or down status of an adjacent system with the Tracked Object Manager. The Extreme Networks BFD solution integrates the BFD application into the Tracked Object Manager through the BFD probe type. This chapter refers to the BFD probe and its configuration. See Tracked Object Manager Configuration for a complete discussion of tracked object probes.

RFC 5880 defines the BFD protocol. RFC 5882 defines BFD interaction with generic applications.

BFD operates in one of two operational modes:

• Asynchronous
• Demand

BFD defaults to the Asynchronous operational mode. When using Asynchronous mode, both peers send periodic Control packets to one another with an application added jitter that over time creates an Asynchronous relationship between the sending and receiving of Control packets.

When using Demand mode, the BFD session has another mechanism to determine if the neighbor is alive, and after an initial interval during which BFD functions in Asynchronous mode, instructs the neighbor to stop sending Control packets.

Both the Asynchronous and Demand modes can use the BFD Echo function. The BFD Echo function tests the forwarding plane by transmitting BFD Echo packets to the neighbor, with the neighbor routing the packet back to the sender via the interface in which the packet was received. The BFD session on the neighbor does not interact with the Echo packets. The Echo Function runs by default and is used in conjunction with a slow-timer, which reduces the frequency of transmitted Control packets from the neighbor to the BFD session. By default, the Echo function operates in conjunction with BFD Asynchronous mode, but can be used as an alternative to the Asynchronous operational mode by turning on Demand mode. The Echo function must be enabled in-order-to turn on Demand mode for the session.

There are minimum transmit and receive Control and Echo packet timing considerations when both Asynchronous mode and the Echo function are used in conjunction with each other. See RFC 5880 for a discussion of these considerations.

Note

Depending upon network configuration, performance numbers will vary. Extreme Networks recommends that you lab test BFD before deploying in a live environment.