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This article shows you how to understand the concept of VXLAN, the content is concise and easy to understand, it will definitely brighten your eyes. I hope you can get something through the detailed introduction of this article.

In addition to the local, flat, and vlan networks discussed earlier, OpenStack also supports vxlan and gre overlay network.

Overlay network refers to a network built on other networks. Nodes in this network can be seen as connected by virtual (or logical) links. Overlay network may consist of several physical links at the underlying level, but for nodes, there is no need to care about these underlying implementations.

For example, the P2P network is overlay network, and so is the tunnel. Both vxlan and gre are implemented based on tunnel technology, and they are also overlay network.

Currently, linux bridge only supports vxlan and does not support both of gre;open vswitch. Vxlan is very similar to the gre implementation, and vxlan is used a lot, so this tutorial only covers vxlan.

VXLAN is called Virtual eXtensible Local Area Network.

As the name suggests, VXLAN provides the same layer 2 Ethernet services as VLAN, but with greater scalability and flexibility. Compared with VLAN, VXLAN has the following advantages:

More layer 2 network segments are supported. VLAN uses 12-bit to mark VLAN ID, supporting up to 4094 VLAN, which can be a bottleneck for large cloud deployments. VXLAN's ID (VNI or VNID) is marked with 24-bit and supports 16777216 layer 2 network segments.

Can make better use of the existing network path. VLAN uses Spanning Tree Protocol to avoid loops, which causes half of the network paths to be dropped by block. VXLAN packets are encapsulated into UDP for transmission and forwarding through three layers, and all paths can be used.

Avoid physical switch MAC table exhaustion. Due to the tunneling mechanism, TOR (Top on Rack) switches do not need to record the information of virtual machines in the MAC table.

VXLAN encapsulation and package format

VXLAN is a network that builds layer 2 on layer 3. Expand the number of layer 2 network segments in the data center by encapsulating layer 2 data into UDP. VXLAN is a solution that supports large-scale multi-tenant network environments in existing physical network facilities. The transport protocol of VXLAN is IP + UDP.

VXLAN defines an encapsulation format for MAC-in-UDP. Add VXLAN header to the original Layer 2 network packet and put it in the UDP and IP packets. With MAC-in-UDP encapsulation, VXLAN is able to establish a Layer 2 tunnel over the Layer 3 network.

VXLAN introduces 8-byte VXLAN header, where VNI accounts for 24-bit. The VXLAN and the original L2 frame are encapsulated in the UDP package.

The VNI of this 24-bit is used to mark different layer 2 network segments and can support 16777216 LAN.

VXLAN Tunnel Endpoint

VXLAN uses VXLAN tunnel endpoint (VTEP) devices to handle the encapsulation and de-encapsulation of VXLAN. Each VTEP has an IP interface configured with an IP address. The IP is used by VTEP to encapsulate the Layer 2 frame, and the encapsulated VXLAN packets are transmitted and received through the IP interface.

VXLAN is independent of the underlying network topology; in turn, the underlying IP network between the two VTEP is also independent of VXLAN. VXLAN packets are routed based on the outer IP header, which uses the VTEP IP on both sides as the source and destination IP.

The above content is how to understand the concept of VXLAN. Have you learned any knowledge or skills? If you want to learn more skills or enrich your knowledge reserve, you are welcome to follow the industry information channel.

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