Bidirectional Forwarding Detection Overview

Bidirectional Forwarding Detection (BFD) is a lightweight hello protocol, with little system overhead, used to rapidly detect link faults without overloading the system. BFD improves network performance by using hardware acceleration for sending packets, resulting in less overheard on the control CPU. BFD works by checking that a device is alive, thus providing rapid detection of the failure of a forwarding path and minimizing traffic loss. BFD can detect the failure of the forwarding plane in a sub-second time interval that is user-configurable.

When BFD is not enabled, packet loss can occur if a delay occurs in detecting that a neighboring device is not operational. Failure in the traffic's forwarding path leads to a traffic black hole, impacting the user experience for applications such as VOIP and video over IP.

Even if multiple protocols are running between the same interfaces, BFD has a single mechanism for detection. Applications that are supported for BFD, such as OSPF, BGP, and static routes, can use BFD to check the liveliness of the next hop for their respective routes installed in the route table manager (RTM). Without BFD, the system can easily become overloaded because such applications need to individually send and receive their hello packets. With BFD, the control protocols between the same endpoints can use a single BFD session, eliminating the requirement to configure aggressive protocol-specific timers. BFD can track the liveliness of a single-hop or multi-hop forwarding engine. Once a BFD session is established, BFD transmits control packets to, and receives control packets from, the session endpoint at a given interval. If BFD packets are not received from the session endpoint for a specified configurable time interval, the session is brought down and the parent application or protocol is notified of the session failure. Upon receipt of such a notification, the respective application looks for an alternate next hop for the route and updates the RTM accordingly.

BFD can be configured for use with the following protocols or applications:

  • OSPFv2
  • OSPFv3
  • BGP4
  • BGP4+
  • IP static routes

BFD is supported for ICX 7850 devices only.

Micro-BFD is supported. Micro-BFD sessions are BFD sessions running on member links of the LAG. Micro-BFD sessions provide BFD with the ability to verify link continuity for every LAG member link. Micro-BFD helps to guarantee the detection of physical member link failures, as well as the overall LAG interface failure.

Multi-hop BFD is supported, providing subsecond forwarding failure detection for a destination with more than one hop and up to 256 hops.

Parent topic: BFD