Association Between the BFD Session Status and the Interface Status
BFD for process interface status (PIS) associates the BFD session status with the interface status. This allows interfaces to be more sensitive to link faults and minimizes the impact of faults on indirectly connected links. When detecting a link fault, a BFD session immediately sends a Down message to the corresponding interface. The interface enters the BFD Down state and only processes BFD packets.
Application
In Figure 1, transit devices are connected through a faulty link. Although they are directly connected at Layer 3, it will take SwitchA and SwitchB a long time to detect the fault because they are connected through multiple physical links. This will increase service interruption time. To prevent this, a BFD session is configured on SwitchA and SwitchB. The BFD session status is associated with the interface status. When a link fault is detected, a BFD session immediately sends a Down message to the corresponding interface and the interface enters the BFD Down state.