How many Virtual Network Identifiers are supported by the VXLAN specification?

The VXLAN (Virtual Extensible LAN) specification, defined in IETF RFC 7348, uses a 24-bit field for the VXLAN Network Identifier (VNI). This 24-bit identifier space allows for a theoretical maximum of 2^24 unique virtual networks. Calculating this value gives 16,777,216 possible VNIs. This large address space is a primary advantage of VXLAN over traditional VLANs, enabling massive scalability required in modern multi-tenant data centers and cloud environments.

A. 4096 is the total number of identifiers (2^12) available with the 12-bit VLAN ID field defined in the IEEE 802.1Q standard.

B. 4094 is the number of usable VLAN IDs in the 802.1Q standard, as VLAN IDs 0 and 4095 are reserved.

D. 16,000,000 is an imprecise approximation and not the exact number of unique identifiers provided by a 24-bit field.

1. IETF RFC 7348: Mahalingam, M., et al. "Virtual eXtensible Local Area Network (VXLAN): A Framework for Overlaying Virtualized Layer 2 Networks over Layer 3 Networks." August 2014.

Reference: Section 5, "VXLAN Header Format," page 6. The document states, "VXLAN Network Identifier (VNI): 24 bits. This is an identifier for the virtual network segment."

2. Arista Networks EOS Documentation: "VXLAN Configuration Guide."

Reference: In the "VXLAN Overview" section, the documentation states: "VXLAN extends the layer 2 segment ID field to 24-bits, which overcomes the 4094 segment limitation of VLANs. With 24-bits, VXLAN can create over 16 million segments."

3. Arista Networks White Paper: "Arista VXLAN Unified Forwarding."

Reference: Page 3. "VXLAN defines a 24-bit network identifier (VNI) which allows for up to 16M virtual L2 networks, overcoming the 4K limitation of VLANs."