What is a four-tier switch

The second-tier switch and the third-tier switch are end-to-end Exchange processes based on port addresses, although this kind of switch technology based on MAC address and IP address can greatly improve the data transmission rate between the nodes, it cannot determine or dynamically restrict the exchange process and data flow of the port according to the application demand of the port host. , that is, the lack of the fourth layer of intelligent application Exchange requirements. Layer Fourth switch can not only complete end-to-end exchange, but also according to the application characteristics of port host, determine or limit its exchange traffic. Simply put, the fourth layer switch is based on the Transport Layer Packet exchange process, is a class of TCP/IP protocol Application layer user application Exchange requirements of a new LAN switch. Layer fourth switches support all protocols below the TCP/UDP layer fourth, identify the packet header length at least 80 bytes, and differentiate the application type of the packet based on the TCP/UDP port number to achieve access control and QoS assurance for the application layer. Therefore, the fourth layer switch is not so much a hardware network device as a software network management system. In other words, layer Fourth switch is a kind of network management Exchange equipment which is mainly software technology and supplemented by hardware technology.

Finally, it is worth pointing out that some people also have some vague concepts, that is, the so-called layer fourth switch is actually on the third layer of switches with the ability to identify the fourth layer of protocol ports, only on the third layer of the switch to add some value-added software only, so not working in the transport layer, It is still on the third layer of exchange operations, but is more sensitive to the third layer of exchange, fundamentally deny the fourth layer of the key technology and the role of exchange. We know that the second-tier ieee802.1p field or third-tier iptos field of the packet can be used to prioritize the packet itself, and we say that layer fourth switches are based on layer fourth packet switching, which is to say that it can analyze the packet application type based on the fourth-tier TCP/UDP port number. That is, layer fourth switches not only fully equipped with all the switching function and performance of the third layer switch, but also can support the intelligent function of network traffic and quality of service control that the third layer switch cannot have.

Important technologies for layer fourth switch support

As mentioned above, the second layer switching device is dependent on the MAC address and the 802.1Q protocol VLAN tag information to complete the link layer Exchange process, the third layer switching/routing device is the IP address information for network path selection to complete the exchange process, The fourth layer switching device is to use the packet header information of the transport layer to help the information exchange and transmission processing. In other words, the exchange information of Layer fourth switch describes the specific content, is essentially a contained in each IP packet all the protocols or processes, such as for Web transport HTTP, FTP for file transfer, Telnet for terminal communication, SSL for secure communication and other protocols. In this way, the fourth-tier exchange protocol that is commonly used in an IP network is actually TCP (for connection based dialogs, such as FTP) and UDP (with connectionless communication, such as SNMP or SMTP) protocols.

Because the headers of TCP and UDP packets include not only the domain "port number", it also indicates what type of network data is being transmitted, and the use of this information (port number) related to a particular application can accomplish a great deal of quality services related to network data and information transmission and exchange, The most notable of these are the following five important application technologies, which are the main technologies commonly used in layer fourth switches.