Bidirectional Forwarding Detection provides sub-second failure detection. It sends frequent, lightweight packets between neighbors. When packets stop arriving, BFD declares the link down.
BFD parameters:
- Interval: How often to send packets (e.g., ms)
- Multiplier: How many missed packets trigger failure (e.g., )
With ms interval and multiplier , detection takes ms.
BFD works with routing protocols, HSRP, VRRP, and static routes. The protocol tells BFD what to monitor. BFD tells the protocol when the neighbor fails.