VXLAN (Virtual Extensible LAN)

Virtual Extensible LAN (VXLAN) is a proposed encapsulation protocol for running an overlay network on existing Layer 3 infrastructure. An overlay network is a virtual network that is built on top of existing network Layer 2 and Layer 3 technologies to support elastic compute architectures. VXLAN will make it easier for network engineers to scale out a cloud computing environment while logically isolating cloud apps and tenants.

A cloud computing architecture is by definition, multi-tenant; each tenant requires its own logical network, which in turn, requires its own network identification (network ID). Traditionally, network engineers have used virtual LANs (VLANs) to isolate apps and tenants in a cloud computing environment but VLAN specifications only allow for up to 4,096 network IDs to be assigned at any given time -- which may not be enough addresses for a large cloud computing environment.

The primary goal of VXLAN is to extend the virtual LAN (VLAN) address space by adding a 24-bit segment ID and increasing the number of available IDs to 16 million. The VXLAN segment ID in each frame differentiates individual logical networks so millions of isolated Layer 2 VXLAN networks can co-exist on a common Layer 3 infrastructure. As with VLANs, only virtual machines (VMs) within the same logical network can communicate with each other.

If approved, VXLAN can potentially allow network engineers to migrate virtual machines across long distances and play an important role in a software-defined networking (SDN), an emerging architecture that allows a server or controller to tell network switches where to send packets. In a conventional network, each switch has proprietary software that tells it what to do. In a software-defined network, packet-moving decisions are centralized and network traffic flow can be programmed independently of individual switches and data center gear. To implement SDN using VXLAN, administrators can use existing hardware and software, a feature that makes the technology financially attractive.

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