What does VXLAN use to uniquely label and identify broadcast domains?

VXLAN (Virtual Extensible LAN) encapsulates Layer 2 frames in Layer 3 packets, creating virtual networks over an existing IP network. To distinguish between these different virtual networks or broadcast domains, VXLAN uses a 24-bit identifier in its header called the Virtual Network Identifier (VNI). Each VNI uniquely identifies a VXLAN segment, allowing for up to 16 million isolated Layer 2 domains on the same physical infrastructure, which is a significant increase over the 4094 limit of traditional VLANs.

A. VLAN ID

A VLAN ID is a 12-bit identifier used in traditional IEEE 802.1Q networks, not the primary identifier for a VXLAN broadcast domain.

B. Agent Circuit Identifier (ACI)

ACI is part of the DHCP Relay Agent Information Option (Option 82) and is unrelated to VXLAN segmentation.

D. End System Identifier (ESI)

ESI is an identifier used in EVPN multihoming to identify a customer edge device connected to multiple provider edge devices.

1. Juniper Networks TechLibrary, "EVPN-VXLAN Overview". This document states, "Each VXLAN is identified by a 24-bit virtual network identifier (VNI), which is also known as the VXLAN segment ID. A VNI uniquely identifies a Layer 2 segment in a VXLAN."

2. RFC 7348, "Virtual eXtensible Local Area Network (VXLAN): A Framework for Overlaying Virtualized Layer 2 Networks over Layer 3 Networks", Section 4. This RFC defines the VNI as the "24-bit ID" used to identify the virtual network segment.