VRF Capacity Calculator
Size VRFs against platform route and VRF limits, with RIB memory and the resource that caps you first.
Inputs
Total Routes Across All VRFs
300,000
FIB Capacity Used
30.00%
VRF Limit Used
5.86%
RIB Memory
71.5MB
VRFs the Platform Really Supports
200
Limiting Resource
FIB route capacity — 1000000 routes runs out at 200 VRFs of this size
Step by step
Values used
VRFs configured = 60 VRFs; Routes per VRF = 5,000 routes; Platform FIB route limit = 1,000,000 routes; Platform VRF limit = 1,024 VRFs; RIB memory per route = 250 bytes
VRF Capacity
Total routes = VRFs × routes per VRF; supportable VRFs is the lower of the VRF table limit and FIB limit ÷ routes per VRF.
Real VRF ceiling
max VRFs = min(VRF limit, FIB limit ÷ routes per VRF).
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
How it works
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).
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.