Analysis on the Main technologies of layer-4 switches

Both layer-2 and layer-3 switches are end-to-end exchange processes based on port addresses. Although this MAC address and IP address-based switch technology can greatly improve the data transmission rate between nodes, however, it is impossible to determine or dynamically limit the port switching process and data traffic according to the port host's application requirements, that is, the fourth layer of intelligent application switching is lacking. The layer-4 switch not only performs end-to-end switching, but also determines or limits the exchange traffic based on the Application Characteristics of the port host. To put it simply, the layer-4 switch is based on the packet exchange process at the transport layer. It is a new type of LAN switch based on the Application exchange requirements at the TCP/IP application layer. The layer-4 switch supports all protocols below the layer-4 of TCP/UDP. It can identify the packet header length of at least 80 bytes and distinguish the application type of data packets based on the TCP/UDP port number, in this way, access control at the application layer and service quality assurance are achieved. Therefore, a layer-4 switch is not so much a hardware network device as a software network management system. That is to say, the layer-4 switch is a kind of network management switching equipment that focuses on software technology and supplemented by hardware technology.

It is worth noting that some people still have some vague concepts to varying degrees, the layer-4 switch adds the ability to identify the layer-4 protocol port on the layer-3 switch, and only adds some value-added software on the layer-3 switch, therefore, it does not work on the transmission layer, but still performs the exchange operation on the third layer. It is only more sensitive to the third layer exchange. It denies the key technology and role of the fourth layer exchange from the root. We know that the layer-2 802.1p field of the data packet or the layer-3 IPToS field can be used to distinguish the priority of the data packet itself. We say that the layer-4 switch is based on the layer-4 Data Packet Exchange, this means that it can analyze the data packet application type based on the layer-4 TCP/UDP port number, that is, the layer-4 switch not only has all the switching functions and performance of the layer-3 switch, it also supports smart functions that are impossible for layer-3 switches to control network traffic and service quality.

Key technologies supported by layer-4 vswitches

As mentioned above, layer-2 switching devices rely on the MAC address and VLAN tag information of the 802.1Q protocol to complete the link layer switching process, layer-3 switching/routing is to use IP address information for network path selection to complete the switching process, the layer-4 switching device uses the packet header information of the transport layer to help information exchange and transmission. That is to say, the specific content described in the switch information of the fourth layer is essentially a protocol or process contained in each IP packet, such as HTTP for WEB transmission and FTP for file transmission, telnet for terminal communication, SSL for secure communication, and other protocols. In this way, in an IP network, the layer-4 Exchange Protocol is actually TCP (for connection-based conversations, such as FTP) and UDP (for connectionless communication, for example, SNMP or SMTP.

Because the packet headers of TCP and UDP packets not only include the domain "port number", it also specifies the type of network data of the packets being transmitted, using this information (Port Number) related to a specific application, you can complete a large number of quality services related to network data and information transmission and exchange, among them, the following five important application technologies are worth noting, because they are the main technologies widely used by layer-4 switches.

BKJIA edit comment]: layer-2 switches perform end-to-end data exchange based on the MAC address table of The Link Layer through routes. layer-3 switches perform end-to-end Switching Based on IP addresses. layer-4 switches can complete end-to-end switching, based on the application characteristics of the port host, it can determine or limit its exchange traffic. Therefore, the industry has a "Application Switch" for the layer-4 switch. Today, with the rapid development of network exchange, 4-layer switches are worth buying.