BFD process-interface-status and process-pst are applicable only for single-hop BFD. Let’s assume that we have two routers directly connected through interface GE1/0/0.
By associating BFD session status with interface status we can trigger fast route convergence. We can use this function only for BFD session that uses a default multicast IP address to detect the single-hop link. We can use association between BFD session status and interface status in the case, when transport devices exist on the link between the routers. As the actual physical path is segmented by transport devices, the routers on both ends need a long time to detect a fault that occurred on the link. The change of BFD status affects the protocol status of the interface and thus fast convergence is triggered. When the BFD session becomes DOWN, the correspondence interface status also goes to BFD_DOWN state, causing that this direct route is deleted from the routing table but the router can still forward BFD packets.
[Labnario] bfd [Labnario-bfd] quit [Labnario] bfd test bind peer-ip default-ip interface gigabitethernet 1/0/0 [Labnario-bfd-session-test] discriminator local 1 [Labnario-bfd-session-test] discriminator remote 2 [Labnario-bfd-session-test] process-interface-status [Labnario-bfd-session-test] commit