GeezerVison

Virtual Extensible Local Area Network (VXLAN) is a network virtualization technology that uses a VLAN-like encapsulation technique to encapsulate OSI layer 2 Ethernet frames within layer 4 UDP datagrams, using 4789 as the default IANA-assigned destination UDP port number,^[1] although many implementations that predate the IANA assignment use port 8472. VXLAN attempts to address the scalability problems associated with large cloud computing deployments.^[2] VXLAN endpoints, which terminate VXLAN tunnels and may be either virtual or physical switch ports, are known as VXLAN tunnel endpoints (VTEPs).^[3][4]

VXLAN addresses the limitations of the VLAN standard for segmenting a physical network into multiple virtual networks. The 12-bit VLAN identifier limits the number of virtual networks on a physical network to 4094. While in some applications, IEEE 802.1ad can be used to extend this limit, this is generally insufficient for large-scale cloud computing infrastructures with many tenants.^[5][6]

VXLAN is an evolution of efforts to standardize on an overlay encapsulation protocol that addresses these issues. Compared to single-tagged IEEE 802.1Q VLANs, which provide a limited number of layer-2 VLANs (4094, using a 12-bit VLAN ID), VXLAN increases scalability up to about 16 million logical networks (using a 24-bit VNID) and allows for layer-2 adjacency across IP networks. Multicast or unicast with head-end replication (HER) is used to flood Broadcast, unknown-unicast and multicast traffic.^[6]

In addition, by encapsulating layer 2 frames in UDP packets, the VXLAN standard also provides for extending a virtual network across multiple geographically distributed physical networks. This is useful for large distributed data centers.^[5]

VXLAN is widely, but not universally, implemented in commercial networking equipment. Several open-source implementations of VXLAN also exist,^[7] including built-in capabilities in the Linux kernel.^[8]

VXLAN is officially documented by the IETF in RFC 7348.^[16] VXLAN encapsulates an Ethernet frame in a UDP datagram for transport across an IP network,^[20] creating an overlay network or tunnel.

Alternative technologies addressing the same or similar operational concerns include:

• IEEE 802.1ad (Q-in-Q), which greatly increases the number of VLANs supported by standard IEEE 802 Ethernet beyond 4K.
• IEEE 802.1ah (MAC-in-MAC), which supports tunneling Ethernet in a way that greatly increases the number of VLANs supported while avoiding a large increase in the size of the MAC address table in a Carrier Ethernet deployment.
• Network Virtualization using Generic Routing Encapsulation (NVGRE), which uses different framing but has similar goals to VxLAN.

• VXLAN Deep Dive: Part 1 and Part 2, November 2012, by Joe Onisick