VxLAN Background

In order to achieve high reliability and redundant deployment, most enterprise networks and their data centers cross multiple physical sites in different physical locations, and deploy similar services at these sites. In order to integrate the data center resources and reduce the management cost, the data center resources are usually virtualized. The virtualization technology of data center mainly includes network virtualization, storage virtualization and server virtualization. Among them, server virtualization is to use special virtualization software to virtualize multiple virtual machines on a physical server. Each virtual machine runs independently and has its own operating system, application program and virtual hardware environment. In order to realize the dynamic resource allocation and management between sites, virtual machines should be able to migrate freely between data centers. Because the migration process of virtual machines is transparent to users, IP address cannot be changed. Therefore, the networks before and after the migration of virtual machines is required to be in the same L2 network. Therefore, it is necessary to realize the interconnection of L2 networks among sites distributed in different places.

VxLAN is a kind of "MAC in IP" technology, which is used to realize the big L2 interconnection based on IP core network. VxLAN only maintains MAC address and forwarding information on the edge devices of the site, without changing the internal network and core network structure of the site.

Using VxLAN as the big L2 network interconnection technology has the following advantages:

• The VxLAN encapsulates the packets sent by the virtual machine in UDP, and uses the IP/MAC address of the physical network as the outer header to encapsulate, which only shows the encapsulated parameters. Therefore, the requirement of the big L2 network   for the MAC address specification is greatly reduced. In addition to vxlan network edge devices, the other devices in the network do not need to identify the MAC address of the virtual machine, which reduces the pressure of MAC address learning and improves the performance of the device.
• The VxLAN introduces a user ID similar to VLAN ID, which is called VxLAN network identifier VNI. It is composed of 24 bits and supports up to 16777215 VxLAN segments, so as to meet a large number of user IDs.
• By using MAC in UDP encapsulation to extend the L2 network, the physical network and virtual network are decoupled. Tenants can plan their own virtual network without considering the limitations of physical network IP address and broadcast domain, which greatly reduces the difficulty of network management.