VRF Capacity Calculator
Size VRFs against platform route and VRF limits, with RIB memory and the resource that caps you first.
About VRF Capacity Calculator
The VRF count a datasheet quotes assumes small VRFs. Because every VRF shares one hardware FIB, the practical limit is set by total prefixes, so 1024 VRFs carrying 5000 routes each needs five million FIB entries no mid-range platform has. FIB exhaustion is an ugly failure: the platform starts punting to software or dropping prefixes silently, and by the time it shows as latency the fix is a hardware replacement rather than a configuration change.
Formulas
VRF Capacity
Total routes = VRFs × routes per VRF; supportable VRFs is the lower of the VRF table limit and FIB limit ÷ routes per VRF.
- FIB
- Forwarding table in hardware — the shared resource every VRF draws from
- routes per VRF
- Average prefix count in each VRF, including the default and any leaked routes
- RIB memory
- Control-plane copy of the routes, roughly 200–400 bytes per prefix per path
Real VRF ceiling
max VRFs = min(VRF limit, FIB limit ÷ routes per VRF).
Worked example
With the default values below, VRF Capacity Calculator returns Total Routes Across All VRFs of 300,000. Change any input above and every figure here is recalculated in your browser.
Inputs used
- VRFs configuredaccepts 1–10,000 VRFs
- 60 VRFs
- Routes per VRFminimum 1 routes
- 5,000 routes
- Platform FIB route limitminimum 1 routes
- 1,000,000 routes
- Platform VRF limitminimum 1 VRFs
- 1,024 VRFs
- RIB memory per routeaccepts 1–4,096 bytes
- 250 bytes
Results
- Total Routes Across All VRFs
- 300,000
- FIB Capacity Used
- 30.00%
- VRF Limit Used
- 5.86%
- RIB Memory
- 71.5 MB
- VRFs the Platform Really Supports
- 200
- Limiting Resource
- FIB route capacity — 1000000 routes runs out at 200 VRFs of this size
Step by step
- 1Values used
- 2VRF Capacity
- 3Real VRF ceiling
- 4Total Routes Across All VRFs= 300,000
- 5FIB Capacity Used= 30.00
- 6VRF Limit Used= 5.86
- 7RIB Memory= 71.5 MB
- 8VRFs the Platform Really Supports= 200
- 9Limiting Resource= FIB route capacity — 1000000 routes runs out at 200 VRFs of this size
Assumptions and limits
- The result is derived only from the 5 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 2 decimal places, 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 VRF Capacity calculated?
Total routes = VRFs × routes per VRF; supportable VRFs is the lower of the VRF table limit and FIB limit ÷ routes per VRF. The VRF count a datasheet quotes assumes small VRFs. Because every VRF shares one hardware FIB, the practical limit is set by total prefixes, so 1024 VRFs carrying 5000 routes each needs five million FIB entries no mid-range platform has.
Why does VRF Capacity matter?
FIB exhaustion is an ugly failure: the platform starts punting to software or dropping prefixes silently, and by the time it shows as latency the fix is a hardware replacement rather than a configuration change.
What values do I need to enter?
This calculator takes 5 inputs: VRFs configured, Routes per VRF, Platform FIB route limit, Platform VRF limit, RIB memory per route. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.