Discussion on the fourth layer switch technology and its application

With the hundred trillion, gigabit, or even the gradual popularization of the LAN, broadband metropolitan area Network, and even wide range of broadband network applications, whether it is intranet, Extranet, also the Community Intelligent Network, expanding the mass of information, is forcing people on the network system of audio, video, Data and other information transmission requirements more and more high. The rapid development of Internet, E-commerce, electronic government affairs, electronic trade, electronic futures and other network trading methods, in the acceleration of logistics, capital flow turnover, but also accelerated the rapid increase in information, to Network Information Center server increased a great deal of pressure, So that the general need to ease the network core system pressure needs a wave higher than a wave. To this end, the industry has to start thinking about the fourth tier Exchange concept to meet the requirements for policy-based networking, Advanced QoS (Quality of Service: Quality of services), and other service improvements. Huge market potential, also greatly stimulated the vast number of manufacturers in the network critical equipment, so that in a very short period of time from the traditional second-tier switches, to technologically advanced third-tier switches, and then to the recent launch of the fourth layer, or even the seventh layer of the product of the gratifying situation.

Layer Fourth switch is different when the third layer switch is, it not only applies the IP Exchange technology in the third layer switch, but more importantly, it stands at a higher level, can view the content of the third layer data header source address and destination address, can take the corresponding action based on the observed information, realizes the bandwidth allocation, Fault diagnosis and key functionality for access control of TCP/IP application data streams. It is clear that layer fourth switches, while using task allocation and load balancing, can optimize the network/server interface, improve the reliability and scalability of the server, and provide detailed traffic statistics and accounting information, so as to solve the network congestion, network security and network management in the level of network application layer, so that the network more " Intelligent "Sex and manageability.

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. The application of high speed LAN has made it easy to integrate the communication types such as voice, video and so on, which are very demanding for delay, jitter and packet loss, and are transmitted on the same data network. From the enterprise network internal security threats, the most ideal preventive measures, is often taken to different users of the right to control, to prevent unauthorized communication. No doubt, all of these require us to have a new LAN switch support. In addition, from improving the quality of service, although we have a continuous increase in network bandwidth this effective and simple method, but regardless of the switch's backplane bandwidth, regardless of the switch packet forwarding rate, no matter how fast the data transmission rate, network congestion is always in the network. This tells us from one side that no quality of service control will also mean that the packet may be lost and the latency may increase.

Visible, the work at higher level, supports the quality service, relies on the software operation and the high-level management the switch, has the important position in the modern enterprise network. The following is a brief introduction to the related performance, technology, application areas and trends of layer fourth switches.

First, what is the fourth layer switch

To understand layer fourth switches, the basic working principles and performance of the traditional second-tier switches and today's widely used third-tier switches are simple to understand, and you can really identify layer fourth switches only through comparison.

It is well known that the second layer switch completes end-to-end data exchange based on the MAC address of the second layer data link layer and the routing through the station table. Because the establishment and maintenance of the station table is automatically completed by the switch, and the router belongs to the third-tier device, the addressing process is based on IP address addressing and routing protocol. Therefore, the second layer of switch is the biggest advantage is the speed of data transmission, because it only needs to identify the MAC address in the frame, and directly based on the MAC address to choose the switch to the originator of the algorithm is very simple, very easy to use ASIC dedicated chip implementation. Obviously, the solution to the second tier switch, actually is a "everywhere exchange" cheap scheme, although this scheme also can divide the subnet, limit the broadcast, the Establishment VLAN, but its control ability is small, the flexibility is not enough, also cannot control each information point the flow, lacks the pan convenient practical routing function.

The third layer switch is to complete end-to-end data exchange directly according to the IP address of the third layer network layer. On the surface, the third layer switch is the second layer exchanger and the router's geereryi, but this kind of union is not the simple physical union, but each takes the director's logical union. An important manifestation of this is that when the first data stream of an information source is exchanged for a third level, the routing system will generate a MAC address and IP address mapping table, and store the table, when the same information source of subsequent data flow into the Exchange environment, the switch will be based on the first generation and save the address map, Directly from the second layer from the source address to the destination address, no longer through the third routing system processing, so as to eliminate the network delay caused by routing, improve the efficiency of packet forwarding, solve the network transmission information between the speed bottleneck. Therefore, the third layer switch can not only complete the port switching function of the second layer switch, but also can complete the routing function of some routers. The switch scheme of the third layer switch, is actually a solution that can support multi-level dynamic integration, although this multi-level dynamic integration can be carried out to some extent by traditional routers and second-tier switches, but this kind of carrying solution requires more device configuration than the three-tier switch, Take up more space, design more wiring and cost more, and data transmission performance is much worse, because in the mass data transmission, the router in the solution cannot overcome the bottleneck of routing transmission rate.

Obviously, the second tier switch and the third layer switch are all based on the port address of the End-to-end exchange process, although this based on MAC address and IP address switch technology, can greatly improve the data transfer rate between the nodes, However, it is not possible to determine or dynamically restrict the exchange process and data traffic of the port based on the application requirements of the port host, that is, the lack of the fourth layer Intelligent application exchange demand. 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 the third-tier IP TOS field in 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 layer 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.