Overlay Network Calculator
Count tunnels in a mesh or hub-and-spoke overlay and work out the goodput left after encapsulation.
Inputs
Tunnels to Maintain
276
Usable Overlay Capacity
95.238Gbps
Encapsulation Overhead
4.76%
Average Capacity per Tunnel
345.07Mbps
Topology Assumed
Full mesh, n(n−1)/2 tunnels
Step by step
Values used
Overlay nodes = 24 nodes; Underlay capacity per node = 100 Gbps; Encapsulation = VXLAN (50 B); Average packet size = 1,000 bytes; Topology = Full mesh
Overlay Network
full mesh tunnels = n(n − 1) ÷ 2, hub and spoke = n − 1; overlay capacity = underlay × payload ÷ (payload + encapsulation).
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
How it works
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
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.