Computer network VLAN Learning

First, we need to understand the origin of VLAN and why such a technology is generated. This starts with the data exchange in the computer network. At the very beginning, our network was in the wild age. How did we exchange data, that is, simple media sharing, and everyone was connected to a line, then send data to each other, which will inevitably lead to a problem. There is only one way for everyone to compete, and there will inevitably be no conflict. The more people you use, the more severe the conflict. Then, we will work out a rule that CSMA/CD is generated. Before sending data, we can check whether the line is busy or not, and then try again. However, there are still some problems. When I was busy, the line was always unavailable to me. I was not happy, and the service was always rejected. What should I do? The second-layer switch comes. Each user allocates a port, binds the MAC address, and uses his/her own port to reduce the conflict. Although L2 switches isolate conflicting domains, they cannot effectively divide broadcast domains. Broadcast packets are sent like all users (ports). When there are too many people, there is still a problem. Although data can be forwarded, it is inefficient and prone to broadcast storms. What should I do? What does a VLAN do? Divide the broadcast domain.

Let's take a look at the professional saying:

What are the advantages of VLAN technology?

No VLAN is defined in TCP/IP specifications. When the second-layer network switch develops to a certain extent, the traditional router's dominance as a network node is greatly challenged due to its insufficient performance. Since traditional routers are bottlenecks in the network and vswitches have such excellent performance, why not replace traditional vrouters to build networks? As we all know, although a vswitch located at Layer 2nd of the Protocol can isolate conflicting domains and improve the performance of each port, it cannot isolate broadcast domains, do not divide subnets, and do not plan networks hierarchically, even more, it is impossible to form a network management policy, because all these features belong to the network layer. Therefore, if only a vswitch is used to construct a large computer network, a huge broadcast domain will be formed. As a result, the network performance is reduced, and the network management is helpless, such a network is unimaginable. According to the TCP/IP principle, generally, the smaller the broadcast domain, the better. Generally, there should be no more than 200 sites. So how can we divide broadcast domains in an exchange network? The designers of the vswitch draw on the concept of the sub-network in the Routing Structure and come up with the concept of virtual network, that is, by dividing IP addresses, MAC addresses, or exchange ports in the network, each part is a virtual local area network that shares a separate broadcast domain. In this way, a large switching network can be divided into multiple independent broadcast domains, namely VLAN.

Let's talk about VLAN, Virtual Local Area Network (Virtual LAN ).

VLAN (Virtual Local Area Network) follows the IEEE 802.1Q standard. It adds four-byte VLAN tags to the Mac field of the original Ethernet frame source. The four-byte Structure

The meanings of fields in VLAN tags are as follows:

Type: The fixed value 0x8100 is used to mark VLAN tags;

User priority: User priority, used for traffic classification;

Flag: The bit is fixed to 0 over Ethernet;

VLAN-ID: 0 ~ 4095, used to mark different VLANs. Let's take a look at how it is implemented:

Because different VLANs are layer-2 isolated, the range of broadcast domains is effectively controlled by assigning different hosts to different VLANs. In this way, the port can be isolated by adding the vlanid above, packet forwarding is relatively orderly, the broadcast domain is reduced, and the conflict is reduced.

More knowledge: http://www.h3c.com.cn/MiniSite/Technology_Circle/Net_Reptile/The_One/Home/Catalog/200911/655250_97665_0.htm

 

Computer network VLAN Learning