Technical Tip: VLAX frame format

Description

This article describes the general frame VXLAN format and its use.

Scope

FortiSwitch.

Solution

While traditional VLAN standards (such as 802.1Q, 802.1ad, and 802.1Q-in-802.1Q) rely on inserting tags directly into the Ethernet frame, VXLAN (Virtual Extensible LAN) introduces a sophisticated network virtualization protocol. It shifts the paradigm from simple tagging to a tunneling architecture, allowing Layer 2 frames to be transported across Layer 3 boundaries.

The core technical distinction of VXLAN lies in its use of UDP encapsulation utilizing the default port 4789. As illustrated in the diagram:

With its 24-bit Network Identifier (VNI), VXLAN provides a massive scaling advantage, supporting up to 16 million virtual networks, a significant upgrade over the 4,094-limit inherent to 802.1Q. This technology is widely deployed in cloud and data center architectures to eliminate traditional segmentation bottlenecks and enable high-density network isolation.