Bidirectional Forwarding Detection (BFD) is a light-weight, low-overhead, short-duration mechanism to detect failures in the path between two systems. If a system stops receiving BFD messages for a long enough period (based on configuration) it is assumed that a failure along the path has occurred and the associated protocol or service is notified of the failure.
The following are the advantages of implementing the BFD mechanism”
used for activity detection over any media type
can be used at any protocol layer
proliferation of different methods and be avoided.
can be used with a wide range of detection times and overhead
BFD is implemented in asynchronous mode, in this mode periodic BFD control messages are used to test the path between the systems.
A path is declared operational when two-way communication has been established between both the systems. A separate BFD session is created for each communication path and data protocol between two systems.
BFD also supports the Echo function defined in draft-ietfbfd-base-04.txt, Bidirectional Forwarding Detection. In this scenario one of the systems send a sequence of BFD echo packets to the other system which loops back the echo packets within the systems forwarding plane. If many of the echo packets are lost, the BFD session is declared as down.