Route Flap Calculator
Apply BGP flap damping: accumulate penalty per flap, compare to the suppress limit and get the suppression time.
About Route Flap Calculator
Damping is an exponential-decay counter per prefix: penalties add up and bleed off over time, and the route is held back while the counter is above the suppress threshold. The penalty ceiling is reuse limit × 2^(max suppress ÷ half-life), which is what stops a badly behaved prefix being suppressed indefinitely. With defaults just two flaps suppress a prefix for around 30 minutes, which is why RFC 7196 and RIPE-580 recommend far higher thresholds — classic damping punishes normal path exploration on multihomed prefixes far harder than intended.
Formulas
Route Flap
Each flap adds a fixed penalty (1000 by default); the penalty decays exponentially with a half-life, and the route is suppressed while it sits above the suppress limit.
- penalty
- Accumulated flap penalty — 1000 per withdrawal by default
- half-life
- Minutes for the penalty to halve, 15 by default
- suppress / reuse
- Suppress at 2000, re-advertise once decay brings it under 750
Exponential decay
Time to reuse = half-life × log2(penalty ÷ reuse limit), capped at the maximum suppress time.
Worked example
With the default values below, Route Flap Calculator returns Accumulated Penalty of 3,000. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Flaps observedaccepts 1–100 flaps
- 3 flaps
- Penalty per flapaccepts 1–20,000
- 1,000
- Half-lifeaccepts 1–240 min
- 15 min
- Suppress limitaccepts 1–60,000
- 2,000
- Reuse limitaccepts 1–60,000
- 750
- Maximum suppress timeaccepts 1–720 min
- 60 min
Results
- Accumulated Penalty
- 3,000
- Route Suppressed
- Yes — penalty 3000 has reached the suppress limit of 2000
- Time Suppressed
- 30.0 min
- Flaps Needed to Trigger Suppression
- 2
- Penalty Ceiling
- 12,000
- Decay
- Penalty halves every 15 min, so it falls back to the reuse limit of 750 after 30 min of stability
Step by step
- 1Values used
- 2Route Flap
- 3Exponential decay
- 4Accumulated Penalty= 3,000
- 5Route Suppressed= Yes — penalty 3000 has reached the suppress limit of 2000
- 6Time Suppressed= 30.0 min
- 7Flaps Needed to Trigger Suppression= 2
- 8Penalty Ceiling= 12,000
- 9Decay= Penalty halves every 15 min, so it falls back to the reuse limit of 750 after 30 min of stability
Assumptions and limits
- The result is derived only from the 6 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 1 decimal place, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
How is Route Flap calculated?
Each flap adds a fixed penalty (1000 by default); the penalty decays exponentially with a half-life, and the route is suppressed while it sits above the suppress limit. Damping is an exponential-decay counter per prefix: penalties add up and bleed off over time, and the route is held back while the counter is above the suppress threshold. The penalty ceiling is reuse limit × 2^(max suppress ÷ half-life), which is what stops a badly behaved prefix being suppressed indefinitely.
Why does Route Flap matter?
With defaults just two flaps suppress a prefix for around 30 minutes, which is why RFC 7196 and RIPE-580 recommend far higher thresholds — classic damping punishes normal path exploration on multihomed prefixes far harder than intended.
What values do I need to enter?
This calculator takes 6 inputs: Flaps observed, Penalty per flap, Half-life, Suppress limit, Reuse limit, Maximum suppress time. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.
Should I enable route flap damping at all?
Only with retuned values. RIPE-580 recommends leaving it off or raising the suppress threshold well above the defaults, because normal BGP path hunting generates enough withdrawals to suppress perfectly healthy prefixes for half an hour.