I. Definition of switch

Switch, which means “switch”, is a network device used for electrical (optical) signal forwarding. It can provide an exclusive electrical signal path for any two network nodes that access the switch. The most common type of switch is the Ethernet switch. Other common ones are telephone voice switches, fiber optic switches, etc.

As an example, a telecommunications broadband network cable is pulled in the university dormitory, and there are 6 people in the dormitory, each with a broadband account, all want to access the Internet, how to make a network cable into 6 network cables? This is the time to use the switch to solve the problem, the switch provides a large number of ports available for cable connection, so that a star topology cabling can be used.

In addition to RJ45 port, the Switch also has SC port for accessing optical fiber, and the PCs connected to the switch can communicate with each other and form a LAN.

Ⅱ.The working process of the switch

When each port is successfully connected, the switch forms a MAC table by corresponding the MAC address to the port. When receiving and sending data later, the packets sent to that MAC address will be sent only from the corresponding port.

After the terminal device is successfully connected to the switch port, the physical address/hardware address (Mac address) of the terminal device, will form a correspondence with the accessed port and be recorded in the MAC table. The packet contains Mac address information, and the switch can send the packet out from the corresponding port according to the address in the packet when transmitting the packet.

III. Three major functions of the switch

(1) Learning

The switch stores the Mac addresses of the connected devices in the Mac table corresponding to the ports.The switch can “learn” the MAC address and store it in the internal address table, so that the data frame can reach the destination address directly from the source address by establishing a temporary switching path between the originator and the target receiver of the data frame.

(2) Forwarding/filtering

Sending to the corresponding port according to the Mac address is sending, and not sending to other ports is filtering.

When the destination address of a data frame is mapped in the MAC address table, it is forwarded to the port of the connected destination node instead of all ports (or to all ports if the data frame is a broadcast/multicast frame).

(3) Loop elimination

When a switch includes a redundant loop, the Ethernet switch avoids the creation of loops through the Spanning Tree protocol while allowing the existence of a fallback path.