Vswitch Technology Application Guide: Build a MAC Address Table

There are many things worth learning about vswitch technology. Here we mainly introduce how to build a MAC address table in vswitch. Switch technology is the focus of network technology. Our network channel has already reported it for readers many times. Because of its importance, we will organize the system again for beginners to refer.

Create a MAC Address Table

Before forwarding data, the switch technology must know the MAC address of the host connected to each of its ports and build a MAC address table. After receiving a data frame from a port, the switch reads the destination MAC address encapsulated in the data frame, and then looks at the previously constructed MAC address table to find the port corresponding to the destination address, data is forwarded from this port, and other ports are not affected. This avoids data collision with other ports. Therefore, building a MAC address table is the top priority of a vswitch. The following is an example of how a vswitch creates an address table.

Assume that host A sends A data frame to host C, and each data frame contains the source MAC address and destination MAC address. When the data frame enters the switch from Port E0, by checking the source MAC address field in the data frame, the switch places the value of host A in the MAC address table and maps it to port E0, indicates that the host to which port E0 is connected is shown in the A11-5 ). At this time, because the MAC address table does not have any entry about the MAC address of the destination MAC address host C. The switch technology forwards this frame to all ports except E0, so that host C can receive this frame. This operation is called flooding ).

The switch forwards data based on the address table.

Similarly, when the switch receives data from host B, host C, and host D, it learns their addresses, writes them to the address table, and maps the corresponding ports to the MAC address. In the end, all the host addresses will be learned to build a complete address table. In this case, if host A sends A data frame to host C again, the switch technology will forward the data frame only from its E2 Port Based on the address ing in its MAC address table. In this way, only host C receives the data frame that host A sends to it, and no longer affects other ports, as shown in Figure 11-6 ). Therefore, when host A communicates with host C, other hosts, such as host B and host D, can also communicate with each other.

After the vswitch establishes a complete MAC address table, the data frame is forwarded by finding the MAC address table to obtain the corresponding port, so that the data frame is sent through a specific port. However, for the broadcast data that enters from a port and the data that cannot find the address entry in the address table, the switch forwards the data frame from all the ports except the incoming port. From this perspective, the devices connected by vswitches are in the same broadcast domain, but they are in different collision domains.

Note: to explain how the vswitch creates a mac address table, assume that A sends A data frame to C. This is not the case. It is not necessary for a communication switch between hosts to learn the MAC address. In fact, when the NIC Driver is loaded, the switch learns the MAC address of the host. If you observe carefully, you will find that the startup process of the Windows system is not complete, and the switch technology will learn the MAC address of the host.