What Is VXLAN & Why It Is So Important in This Cloud Era

What is VXLAN? VXLAN stands for Virtual Extensible LAN and is a widely used network virtualization technology in large Layer 2 networks. It was developed to address a series of issues in virtualization during the era of cloud computing.

What is VXLAN?

A logical VXLAN tunnel is established between the source and destination network devices using MAC in UDP (User Datagram Protocol) encapsulation. In other words, the original Ethernet packet sent by a virtual machine is encapsulated within a UDP packet, and then the outer layer is encapsulated with the IP packet header and Ethernet packet header of the physical network. This way, the encapsulated packet behaves like a normal IP packet and can be forwarded through the routing network. It's like giving virtual machines in the Layer 2 network the wings of routing, allowing them to break free from the structural limitations of Layer 2 and Layer 3 networks. 

Why is VXLAN needed?

This is closely related to the virtualization trend on the server side of data centers. On the one hand, server virtualization introduced dynamic VM migration, which requires a network that provides seamless access.

On the other hand, data centers have grown in scale with a significant increase in the number of tenants, necessitating a network that can isolate a massive number of tenants. VXLAN can meet these two key requirements.

The VXLAN network introduces the following new elements compared to traditional networks:

1. VTEP (VXLAN Tunnel Endpoints): These are the edge devices in the VXLAN network and serve as the starting and ending points of VXLAN tunnels. All related processing of VXLAN packets is performed on VTEPs. In summary, VTEP is an essential component in the VXLAN network. It can be either a standalone network device (such as Huawei's CE series switches) or a server hosting virtual machines. Its role will be revealed shortly.

2. VNI (VXLAN Network Identifier): As mentioned earlier, VLANs in Ethernet frames occupy only 12 bits, which limits their isolation capability in data center networks. The introduction of VNI specifically addresses this problem. VNI is a user identifier similar to VLAN ID, where each VNI represents a tenant and virtual machines with different VNI values cannot directly communicate at Layer 2. When encapsulating VXLAN packets, sufficient space is allocated to VNI to support the isolation of a massive number of tenants. The detailed implementation will be explained later in the document.

3. VXLAN Tunnel: "Tunnel" is a logical concept that is not new, such as the well-known Generic Routing Encapsulation (GRE). In simple terms, it transforms the original packet by encapsulating it, enabling it to be transmitted over a transport network (such as an IP network). From the perspective of the host, it appears as if there is a direct link between the source and destination of the original packet. This seemingly direct link is the "tunnel." As the name suggests, a "VXLAN tunnel" is used to transport VXLAN encapsulated packets and represents a virtual channel established between two VTEPs.

What are the differences between VLAN and VXLAN?

What is VXLAN? VLAN (Virtual LAN) and VXLAN (Virtual Extensible LAN) are network virtualization technologies used in Layer 2 networks. While both serve the purpose of network segmentation and isolation, they differ in several key aspects.