Analysis of the fourth layer switch technology

In recent years, with the hundred trillion, gigabit, even the gradual popularization of gigabit LAN, broadband LAN, and even wide range of bandwidth network applications, driving the development of the exchange technology. Enterprise applications, the rapid development of the Internet, E-commerce, e-government, electronic trade, electronic futures, such as the use of network transactions, in the acceleration of logistics, capital flow turnover, but also accelerated the rapid increase in information, the Network Information Center server increased the great pressure. In the face of a wave higher than a wave of network core system pressure mitigation requirements, the emergence of the fourth layer switch is inevitable.

What is layer fourth switch

Layer Fourth switch is a switch product developed with the fourth layer Exchange technology, of course it works on the fourth layer of the OSI/RM model, that is, the transport layer, directly facing the concrete application. From the functional point of view, rather than the fourth layer switch is a hardware network equipment, it is better to say that it is a software network management system, in other words, is a class of software technology-oriented, hardware technology as a supplement to the network management Exchange equipment. Layer fourth switches support all protocols below the TCP/UDP layer fourth, such as Http,ftp, Telnet, SSL, and so on, to identify at least 80 bytes of packet header length, depending on the TCP/UDP port number to distinguish the application type of the packet, In order to achieve the application layer access control and quality of service assurance.

Many people are confused when it comes to distinguishing between the fourth-tier switch and the third-tier switch principle. The so-called layer fourth switch is actually added to the third tier switch with the ability to identify the layer Fourth protocol port, adding some value-added software only to the third tier switch, not working on the transport layer, Instead, the exchange operation is still on the third layer. The layer fourth switch is based on the TCP/UDP port number to differentiate packets, that is, the fourth layer switch not only fully equipped with all the switching functions and performance of the third layer switch, but also to support the third layer of the switch is not possible to have network traffic and quality of service control intelligent functions.

Important technologies for layer fourth switch support

Unlike the second tier switching device, which relies on the MAC address and the 802.1Q protocol VLAN tag to complete the link layer exchange process, it is also different from the third layer switching/routing device to use 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. That is, all the protocols or processes in each IP packet, so the layer Fourth Exchange protocol used is TCP (for connection based dialogs, such as FTP) and UDP (with connectionless communication, such as SNMP or SMTP) these two protocols.

Because the headers of TCP and UDP packets can indicate the type of packet being transmitted, the use of information (port number) related to a particular application can accomplish a large number of quality services related to network data and information transmission and exchange. Five of these technologies are critical and are the main technologies commonly used in layer fourth switches.

First, packet filtration/safety control:

Unlike traditional software-based routers, the main difference between the fourth-tier exchange and the third-tier exchange is that the filtering capability is implemented in ASIC-specific high-speed chips, so that the safe filter control mechanism can be carried out in full speed and greatly improve packet filtration rate. Using layer fourth information to define filtering rules has become the default standard for general routers, not only to allow or disallow links between IP subnets, but also to control the communication of specified TCP/UDP ports.

Second, the quality of service:

In the hierarchical structure of the network system, the information of the fourth layer is often used to establish the application-level communication priority tcp/udp. For example, the port number of a packet in TCP/UDP is exchanged. It allows a certain amount of bandwidth to be used for important applications based on the priority of the application's partitioning of communication data, depending on the level of traffic of a particular application. In a sense, layer fourth Exchange provides a way to implement service levels (COS) in the network. This allows for an intranet to reduce the amount of traffic on WWW or FTP, and to set higher priority for e-mail or telent traffic. Therefore, layer fourth switches are particularly important based on this functionality. If, in the case of communications, the lack of a fourth layer of information is hampered by the absence of priority, the urgent application of rapid transmission on the network will be greatly discouraged.

Third, server load balancing:

The server load balancing supported by layer fourth switches is the IP address that will be attached with the load Balancing service, consisting of a group of different physical servers and a virtual IP address (VIP) for each server group for search. Each application server address stored in the Domain name server (DNS) is a VIP, not a real server address. When a user applies for an application, a VIP connection request (such as a TCPSYN packet) with the target server group is sent to the server switch. The server switch selects the best server in the group, replaces the VIP in the terminal address with the IP of the actual server, and only after the network address translation (NAT) that is performed through the switch can the server with the unregistered IP address be able to gain access. The benefits of preventing unauthorized access can be achieved through such a setting.

Four, host standby connection:

The host standby connection provides a redundant connection to the port device, thereby effectively protecting the system when the switch fails. Because of the shared MAC address, the backup switch receives the same data as the primary unit, which enables the backup switch to monitor the communication content of the primary switch service. The primary switch continuously notifies the backup switch of the fourth tier of relevant data, MAC data, and its power status. When a primary switch encounters a failure, the backup switch is automatically taken over and no conversation or connection is interrupted.

V. Statistics:

Layer fourth switches are able to provide more detailed statistical records by querying the layer fourth packet. This allows the administrator to collect more detailed information about which IP address is being communicated as needed, and even to collect communication information based on which application tier service is involved in the communication. These statistics are especially effective for examining the load on each application on the server, such as viewing the system resources occupied by a service application.

Conclusion:

The fourth layer Exchange technology has obvious advantages over the original second layer and the third layer switching technology. It is different from the router or the third tier exchange, only for a single package processing, it is not clear where the last package from, also do not know the next package, only based on the TCP port number in the packet header to establish a priority queue, by the router based on the link and network available nodes to determine the route While layer fourth switches are based on the available servers and performance to determine the interval first.

Now, the establishment of a high-speed, broadband, stable, reliable, and can fuse security and confidentiality of the new requirements of the internal and external network system, is the current enterprise network development trend. Driven by the enormous market potential, more manufacturers are committed to producing better, more advanced fourth-tier exchanger products, and even the seventh-tier switch products such a cheerful situation is also the trend, which will further promote the development of network application technology.