Overlay Network Calculator
Count tunnels in a mesh or hub-and-spoke overlay and work out the goodput left after encapsulation.
About Overlay Network Calculator
Tunnel count in a full mesh grows quadratically, which is why 24 nodes need 276 tunnels and 100 nodes need 4950. Capacity is scaled by the payload fraction of the encapsulated frame. Tunnel count drives control-plane state, IKE rekey load and configuration size, and it is the usual reason a full mesh has to become a hub-and-spoke or route-reflector design.
Formula
Overlay Network
full mesh tunnels = n(n − 1) ÷ 2, hub and spoke = n − 1; overlay capacity = underlay × payload ÷ (payload + encapsulation).
- n
- Number of overlay endpoints (VTEPs, SD-WAN edges or VPN peers)
- encapsulation
- Bytes added per packet — 24 for GRE, 50 for VXLAN, up to 73 for IPsec
Worked example
With the default values below, Overlay Network Calculator returns Tunnels to Maintain of 276. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Overlay nodesaccepts 2–5,000 nodes
- 24 nodes
- Underlay capacity per nodeaccepts 0.001–800 Gbps
- 100 Gbps
- Encapsulationone of GRE (24 B), VXLAN (50 B), Geneve, no options (50 B), Geneve with 16 B options (66 B), WireGuard (60 B), IPsec ESP tunnel, AES-CBC + SHA (73 B)
- VXLAN (50 B)
- Average packet sizeaccepts 64–9,000 bytes
- 1,000 bytes
- Topologyone of Full mesh, Hub and spoke
- Full mesh
Results
- Tunnels to Maintain
- 276
- Usable Overlay Capacity
- 95.238 Gbps
- Encapsulation Overhead
- 4.76%
- Average Capacity per Tunnel
- 345.07 Mbps
- Topology Assumed
- Full mesh, n(n−1)/2 tunnels
Step by step
- 1Values used
- 2Overlay Network
- 3Tunnels to Maintain= 276
- 4Usable Overlay Capacity= 95.238 Gbps
- 5Encapsulation Overhead= 4.76
- 6Average Capacity per Tunnel= 345.07 Mbps
- 7Topology Assumed= Full mesh, n(n−1)/2 tunnels
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 3 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 Overlay Network calculated?
full mesh tunnels = n(n − 1) ÷ 2, hub and spoke = n − 1; overlay capacity = underlay × payload ÷ (payload + encapsulation). Tunnel count in a full mesh grows quadratically, which is why 24 nodes need 276 tunnels and 100 nodes need 4950. Capacity is scaled by the payload fraction of the encapsulated frame.
Why does Overlay Network matter?
Tunnel count drives control-plane state, IKE rekey load and configuration size, and it is the usual reason a full mesh has to become a hub-and-spoke or route-reflector design.
What values do I need to enter?
This calculator takes 5 inputs: Overlay nodes, Underlay capacity per node, Encapsulation, Average packet size, Topology. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.