BFD timer calculator
Enter both systems' BFD intervals and Detect Mult to get, for each direction, the agreed transmit interval, its jitter range, the detection time the receiver computes and whether Echo may run, every number explained with its RFC 5880 section; or paste a BFD Control packet in hex to decode it field by field.
Réseau| Field | System A | System B |
|---|---|---|
| Desired Min TX Interval | ||
| Required Min RX Interval | ||
| Detect Mult | ||
| Required Min Echo RX Interval (optional) | ||
| Demand mode |
Intervals take a unit: us (or µs), ms or s, as in 300ms, 300000us or 1s; the protocol itself carries microseconds. A Required Min RX of 0 asks the other system to send no periodic packets, and an empty or zero Required Min Echo RX refuses to loop Echo packets.
Runs entirely in your browser: the arithmetic of RFC 5880, no network, no clock.
Everything is computed in your browser from the numbers you enter, by the rules of RFC 5880: in each direction the agreed transmit interval is the larger of the sender's Desired Min TX and the receiver's Required Min RX (sections 6.8.2 and 6.8.7), each interval is shortened by a random 0 to 25% (10 to 25% with a Detect Mult of 1), and the receiver's detection time is the sender's Detect Mult times that interval in Asynchronous mode, or its own Detect Mult times its own agreed transmit interval in Demand mode (section 6.8.4). While the session is not Up every Desired Min TX is raised to one second (section 6.8.3). Echo follows section 6.8.9 and RFC 5883 section 3; Common Intervals follow RFC 7419. Implementation floors are reported only where a vendor document states one. The packet decoder reads the RFC 5880 section 4.1 layout and applies the section 6.8.6 receive checks. Behaviour is pinned by 42 golden vectors.
- RFC 5880 (BFD)The packet fields, the timer negotiation, jitter, the detection time, the slow start, Demand mode, Echo and the receive checks
- RFC 5881 (BFD single hop)UDP ports 3784 and 3785 and the TTL of 255
- RFC 5883 (BFD multihop)UDP port 4784 and no Echo over multiple hops
- RFC 7419 (Common Interval Support in BFD)The Common Interval set, the 10 s graceful-restart interval and adjustment towards larger intervals
- FRRouting documentation, BFD (bfdd)The 10 ms floor of receive-interval, transmit-interval and echo receive-interval, the defaults, and the worked examples the golden vectors reproduce
- Junos OS 13.1, bfd-liveness-detection (2013)The 1 to 255,000 ms range of minimum-interval in that release
- IANA BFD ParametersDiagnostic code 9 and authentication types 6 to 8 the decoder names