BFD
Bidirectional Forwarding Detection (BFD) is a low-overhead, short-duration method for detection of failures in the path between adjacent forwarding engines, including the interfaces, data link(s), and, to the extent possible, the forwarding engines themselves. It also provides a single mechanism that can be used for liveness detection between a pair of devices over any media, at any protocol layer, with a wide range of Detection Times and overhead, to avoid proliferation of different methods. BFD operates in two modes:
- Asynchronous mode: In this mode, an operating device periodically sends BFD control packets. If the device does not receive BFD control packet from the peer within the specified interval, it tears down the BFD session.
Demand mode: in this mode, it is assumed that an operating device has an independent way of verifying that it has connectivity to the peer. Once a BFD session is established, one device may requrest that the other device stops sending BFD control packets, except when the connection needs to be explicity validated, in which case a short sequence of BFD Control packets is exchanged. Demand mode may operate independently in each direction, or simultaneously.