VXLAN Overlay Header Utility

VXLAN Header & VNI Decoder

Decode an 8-byte VXLAN header and inspect the flags field, VNI-valid I bit, reserved bits, 24-bit VXLAN Network Identifier, hexadecimal VNI value and reserved header bytes.

✓ 8-Byte Header ✓ 24-bit VNI ✓ I Bit ✓ Reserved Bits ✓ Decimal / Hex VNI ✓ Header Validation

VNI

VXLAN Header Decode

● Ready

VXLAN Header Hex Bytes Enter the standard 8-byte VXLAN header beginning at the VXLAN Flags field. Spaces, commas, colons, hyphens, line breaks, continuous hexadecimal and 0x-prefixed bytes are accepted.

Header Length Trailing mode decodes the first eight bytes and reports any remaining data.

Reserved Field Validation In a conventional VXLAN header, reserved flag bits and reserved bytes are zero.

Standard VXLAN header: the header is eight bytes. Bit 0x08 in the first flags byte is the VNI-valid I bit. The VNI itself occupies bytes 4, 5 and 6 in network byte order, providing a 24-bit numeric range from 0 through 16,777,215.

VXLAN Header Decode Result Header Decoded

Decoded VXLAN Header —

Flags Byte —

I Bit —

VNI Decimal —

VNI Hex —

VNI Binary —

Reserved Bytes 1–3 —

Reserved Byte 7 —

Standard Flags —

Header Bytes —

Trailing Bytes —

VNI Valid —

Header Status —

Header Fields —

Bit-Level Breakdown —

Trailing Data —

Validation —

What Is a VXLAN Header?

VXLAN, or Virtual eXtensible Local Area Network, encapsulates Layer 2 Ethernet traffic inside UDP. A standard VXLAN encapsulation places an eight-byte VXLAN header between the outer UDP header and the encapsulated Ethernet frame.

The main identifier in the header is the 24-bit VXLAN Network Identifier, usually called the VNI.

VXLAN Header Format

Byte 0:
Flags

Bytes 1–3:
Reserved

Bytes 4–6:
VXLAN Network Identifier (VNI)

Byte 7:
Reserved

Total:
8 bytes

VXLAN Flags Byte

In the conventional VXLAN header, the VNI-valid I bit corresponds to hexadecimal mask 0x08.

Standard Flags:

00001000
   ↑
   I bit

Hex:
08

When the I bit is set, the VNI field is valid. Reserved flag bits are expected to remain zero in the standard VXLAN format.

What Is a VXLAN VNI?

VNI means VXLAN Network Identifier. It identifies the VXLAN overlay segment to which the encapsulated Ethernet frame belongs.

The VNI occupies 24 bits, allowing a substantially larger segmentation space than the 12-bit VLAN ID field used by IEEE 802.1Q VLAN tagging.

VXLAN VNI Range

VNI width:
24 bits

Raw numeric range:
0 to 2^24 - 1

Maximum:
16,777,215

Hex maximum:
0xFFFFFF

The raw header can represent the complete 24-bit range, although operational deployments may apply additional conventions or restrictions.

How Is the VNI Decoded?

The three VNI bytes are interpreted in network byte order, with the first byte being the most significant.

VNI Bytes:

00 13 88

Calculation:

(0x00 << 16)
+
(0x13 << 8)
+
0x88

= 0x001388
= 5000

VXLAN Header Example

08 00 00 00 00 13 88 00

08
Flags
I = 1

00 00 00
Reserved

00 13 88
VNI = 5000

00
Reserved

VXLAN Reserved Fields

The standard VXLAN header reserves most of its non-VNI bits. Reserved bits and bytes are normally transmitted as zero and ignored when received according to the base header rules.

Extensions or VXLAN-related variants can define additional semantics, so this tool deliberately identifies itself as a decoder for the standard base VXLAN header rather than treating every eight-byte VXLAN-related format as identical.

VXLAN vs VLAN

Feature	VLAN	VXLAN
Segment Identifier	VLAN ID	VNI
Identifier Width	12 bits	24 bits
Raw ID Space	4,096 values	16,777,216 values
Transport	Ethernet tagging	Overlay over UDP/IP

VXLAN UDP Encapsulation

A complete VXLAN packet normally includes an outer Ethernet frame, IP header, UDP header, VXLAN header and an encapsulated inner Ethernet frame.

Outer Ethernet
↓
Outer IP
↓
UDP
↓
VXLAN Header
↓
Inner Ethernet
↓
Inner Payload

This page decodes only the eight-byte VXLAN header and does not attempt to parse the surrounding IP, UDP or inner Ethernet headers.

VXLAN Header & VNI Decoder FAQs

How many bytes is a standard VXLAN header?

The base VXLAN header is eight bytes long.

How many bits is a VXLAN VNI?

The VXLAN Network Identifier occupies 24 bits, or three bytes.

What is the maximum raw VNI value?

The largest unsigned 24-bit value is 16,777,215, which is hexadecimal 0xFFFFFF.

What does 0x08 mean in a VXLAN header?

In the standard VXLAN flags byte, 0x08 means the I bit is set, indicating that the VNI field is valid.

Where is the VNI stored?

The VNI occupies bytes 4 through 6 of the eight-byte VXLAN header when byte 0 is counted as the first flags byte.

Does VXLAN use UDP?

Yes. Standard VXLAN encapsulates the VXLAN header and inner Ethernet frame inside UDP over an outer IP network.

Does this tool decode the inner Ethernet frame?

No. This tool solves only the VXLAN Header and VNI decoding task. Bytes after the first eight can be displayed as trailing data but are not interpreted as an Ethernet frame.