What is BFD?
BFD (Bidirectional Forwarding Detection) is a protocol for rapid bidirectional link failure detection between two devices. It operates independently of routing protocols.
How BFD Works
- Devices exchange short control messages (Hello packets)
- If several consecutive messages are lost, the link is considered down
- This information is sent to the router, which quickly reroutes traffic
BFD Features
- Detection intervals starting from milliseconds
- Works over any protocol: OSPF, BGP, IS-IS, static routes
- Minimal resource consumption
Use Cases
- Failure detection in L3 and L2 links
- Protection of high-availability routes
- Faster convergence of IGP and BGP
Example
| Parameter | Value |
|---|---|
| Hello Interval | 50 ms |
| Detection Timer | 150 ms |
| Link Failure Detection | Less than 0.2 sec |
FAQ
How is BFD better than regular keepalives?
It’s faster and lighter, and doesn’t require full routing packet processing.
Can it be used with MPLS?
Yes, BFD supports MPLS LSP and works with LDP, RSVP, and Segment Routing.
Does it require a license?
Depends on the vendor.
Conclusion
BFD ensures minimal link failure detection time, which is critical for carrier-grade and high-availability network architectures.
