The development of the two-layer switching technology is relatively mature. The two-layer industrial switch is a data link layer device. It can identify the MAC address information in the data packet, forward it according to the MAC address, and record these MAC addresses and corresponding ports in its own internal An address table.

The specific workflow is as follows:

1) When the industrial switch receives a data packet from a certain port, it first reads the source MAC address in the packet header, so that it knows which port the machine with the source MAC address is connected to;

2) Read the destination MAC address in the header, and look up the corresponding port in the address table;

3) If there is a port corresponding to the destination MAC address in the table, copy the data packet directly to this port;

4) If the corresponding port is not found in the table, the data packet will be broadcast to all ports. When the destination machine responds to the source machine, the industrial switch can record which port the destination MAC address corresponds to, and the next time the data is transmitted It is no longer necessary to broadcast to all ports. This process is repeated continuously, and the MAC address information of the entire network can be learned. This is how the Layer 2 switch establishes and maintains its own address table.

The reason why the Layer 2 switch is so efficient is that on the one hand, its hardware realizes high-speed forwarding, and on the other hand, because the Layer 2 switch only reads the encapsulated data packet, and does not modify the data packet (the router will To modify, modify its destination and source MAC address).