Dell PowerEdge FN I/O Module Configuration Guide 9.10(0.0)

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 eliminates 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, BFD agents maintain sessions that reside on the line card, which frees resources on the route processor module (RPM). Only session state changes are reported to the BFD Manager (on the RPM), which in turn notifies the routing protocols that are registered with it.

BFD is an independent and generic protocol, which all media, topologies, and routing protocols can support using any encapsulation. Dell Networking has implemented BFD at Layer 3 and with user datagram protocol (UDP) encapsulation. BFD functionality will be implemented in phases. OSPF, IS-IS, VRRP, VLANs, LAGs, static routes, and physical ports support BFD, based on the IETF internet draft draft-ietf-bfd-base-03.