VXLAN Calculator
Calculate VXLAN encapsulation overhead and VNI address space.
About VXLAN Calculator
VXLAN wraps each original (inner) Ethernet frame inside a new outer packet: an 8-byte VXLAN header identifying the virtual network, an 8-byte UDP header, a 20-byte outer IPv4 header, and a 14-byte outer Ethernet header — 50 bytes of overhead in total. Because the encapsulated frame must still fit within the physical network's MTU, the effective usable MTU for guest/inner traffic is the physical MTU minus this overhead, which is why VXLAN deployments commonly require jumbo frames (MTU 1600+ or 9000) on the underlay to avoid fragmenting normal 1500-byte guest frames. Separately, VXLAN's 24-bit VNI field supports over 16 million isolated virtual networks, vastly more than the 4096 VLANs traditional 802.1Q tagging allows.
Formulas
Effective MTU
effective_mtu = physical_mtu − 50
Max VNIs
max_vnis = 2^24 = 16,777,216
Worked example
With the default values below, VXLAN Calculator returns Effective Inner (Guest) MTU of 1,450. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Physical (Underlay) MTUminimum 576 bytes
- 1,500 bytes
Results
- Effective Inner (Guest) MTU
- 1,450 bytes
- VXLAN Encapsulation Overhead
- 50 bytes
- Max VXLAN Network Identifiers (VNIs)
- 16,777,216
- Overhead as % of Physical MTU
- 3.33%
Step by step
- 1Values used
- 2Effective MTU
- 3Max VNIs
- 4Effective Inner (Guest) MTU= 1,450 bytes
- 5VXLAN Encapsulation Overhead= 50 bytes
- 6Max VXLAN Network Identifiers (VNIs)= 16,777,216
- 7Overhead as % of Physical MTU= 3.33
Assumptions and limits
- The result is derived only from the single input 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
Why is jumbo frame support recommended for VXLAN?
With a standard 1500-byte physical MTU, VXLAN's 50-byte overhead leaves only 1450 bytes for the inner frame — below the standard 1500-byte Ethernet MTU guest VMs expect, which forces fragmentation or requires the guest OS to use a smaller MTU. Enabling jumbo frames (e.g. 1600+ or 9000-byte MTU) on the physical underlay avoids this by leaving enough headroom to encapsulate a full-size 1500-byte guest frame without fragmentation.
Why does VXLAN support so many more networks than VLANs?
Traditional 802.1Q VLAN tags use a 12-bit ID field, capping the address space at 4096 VLANs — insufficient for large multi-tenant cloud environments. VXLAN's VNI field is 24 bits, providing over 16.7 million possible network identifiers, which is why VXLAN became the standard overlay technology for cloud-scale network virtualization.
Does VXLAN overhead affect application-layer throughput?
Yes, marginally — the 50 bytes of overhead per packet reduces the payload-to-overhead ratio for small packets more than large ones, and if fragmentation occurs due to insufficient underlay MTU, throughput can degrade significantly more than the raw overhead percentage suggests, since fragmentation/reassembly adds CPU cost and potential packet loss.