Bidirectional Forwarding Detection (BFD) is a detection protocol designed to provide fast forwarding path failure detection
times for all media types, encapsulations, topologies, and routing protocols and independent of the higher layer protocols.
In addition to fast forwarding path failure detection, BFD provides a consistent failure detection method for network administrators.
Because the network administrator can use BFD to detect forwarding path failures at a uniform rate, rather than the variable
rates for different routing protocol hello mechanisms, network profiling and planning is easier and reconvergence time is
consistent and predictable.
Protocol Independent Multicast (PIM) uses a hello mechanism for discovering new neighbors and for detecting failures between
adjacent nodes. The minimum failure detection time in PIM is 3 times the PIM Query-Interval. To enable faster failure detection,
the rate at which a PIM Hello message is transmitted on an interface is configurable. However, lower intervals increase the
load on the protocol and can increase CPU and memory utilization and cause a system-wide negative impact on performance. Lower
intervals can also cause PIM neighbors to expire frequently as the neighbor expiry can occur before the hello messages received
from those neighbors are processed.
The BFD Support for Multicast (PIM) feature, also known as PIM BFD, registers PIM as a client of BFD. PIM can then utilize
BFD to initiate a session with an adjacent PIM node to support BFD's fast adjacency failure detection in the protocol layer.
PIM registers just once for both PIM and IPv6 PIM.
At PIMs request (as a BFD client), BFD establishes and maintains a session with an adjacent node for maintaining liveness
and detecting forwarding path failure to the adjacent node. PIM hellos will continue to be exchanged between the neighbors
even after BFD establishes and maintains a BFD session with the neighbor. The behavior of the PIM hello mechanism is not altered
due to the introduction of this feature.
Although PIM depends on the Interior Gateway Protocol (IGP) and BFD is supported in IGP, PIM BFD is independent of IGP's