Bidirectional Forwarding Detection (BFD) is an efficient, short-duration detection of 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.
BFD can provide a mechanism used for failure detection over any media, at any protocol layer, with a wide range of detection times and overhead, to avoid a proliferation of different methods.
SR OS supports asynchronous and on-demand modes of BFD in which BFD messages are sent to test the path between systems.
If multiple protocols are running between the same two BFD endpoints, only a single BFD session is established, and all associated protocols share the single BFD session.
As well as the typical asynchronous mode, there is also an echo function defined within RFC 5880, Bidirectional Forwarding Detection, that allows either of the two systems to send a sequence of BFD echo packets to the other system, which loops them back within that system’s forwarding plane. If a number of these echo packets are lost, the BFD session is declared down.