VXLAN Calculator
Calculate VXLAN encapsulation overhead, effective MTU, and maximum VNI address space.
Inputs
MTU of the underlying physical network (1500 standard, 9000 for jumbo frames)
Effective Inner (Guest) MTU
1,450bytes
VXLAN Encapsulation Overhead
50bytes
Max VXLAN Network Identifiers (VNIs)
16,777,216
Overhead as % of Physical MTU
3.33%
Step by step
Values used
Physical (Underlay) MTU = 1,500 bytes
Effective MTU
effective_mtu = physical_mtu − 50
Max VNIs
max_vnis = 2^24 = 16,777,216
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
How it works
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
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.