In-depth analysis of layer-4 switch application

The layer-4 switch is quite common. So I studied the practical application of the layer-4 switch and shared it with you here. I hope it will be useful to you. With the increasing popularity of Mbit/s, Gbit/s, and even Mbit/s local area networks, broadband MAN networks and even broadband wide area networks are widely used. Whether it is Intranet, exclusive, or residential intelligent networks, it is increasingly expanding to massive amounts of information, it is forcing people to transmit audio, video, data and other information in the network system more and more demanding.

With the rapid development of Internet, the use of e-commerce, e-government, e-trade, e-futures and other online trading methods accelerates logistics and capital flow turnover while accelerating the rapid increase of information, this puts a great deal of pressure on the Network Information Center servers, so that the general need to ease the pressure on the network core system is too high. To this end, the industry has to begin to consider the fourth-layer switch concept to meet the requirements of policy-based networking, advanced QoSQuality of Service: Service quality) and other Service improvements. The huge market potential has greatly stimulated significant investment by manufacturers in key network equipment, so that in a very short period of time, the emergence of a traditional second-layer switch, to the Advanced Layer-3 Switch, to the latest layer-4 or even layer-7 switch product.

When a layer-4 switch differs from a layer-3 switch, it not only applies the IP exchange technology in the layer-3 switch, but also stands at a higher level, you can view the content of the source address and destination address of the third-level data packet header. You can take corresponding actions based on the observed information, implement the key functions of bandwidth allocation, fault diagnosis, and access control over TCP/IP application data streams. Obviously, layer-4 switches can optimize the network/server interface while assigning tasks and balancing loads to improve server reliability and scalability, it also provides detailed traffic statistics and accounting information to solve network congestion, network security, and network management issues at the network application layer level, making the network more "intelligent" and manageable.

Establishing an internal external network system that is high-speed, broadband, stable, reliable, and able to integrate new demands such as security and confidentiality is the current trend of enterprise network development. High-speed LAN applications have easily integrated voice, video, and other communication types that require high latency, jitter, and packet loss into the same data network for transmission. The most ideal preventive measure for security threats within the enterprise network is to control the permissions of different users to prevent unauthorized communication. Do not be suspicious. All of these require the support of all-new LAN switches. In addition, from the perspective of improving service quality, although we have an effective and simple method of increasing network bandwidth, no matter how high the bandwidth of the vswitch's backboard, no matter how big the packet forwarding rate of the vswitch is, no matter how fast the data transmission rate is, network congestion always exists in the network. This tells us from one side that the absence of Service Quality Control also means that data packets may be lost and the latency may increase. It can be seen that working on switches at a higher level, supporting quality services, relying on software operation and high-level management is an important position in modern enterprise networks. Next we will briefly introduce the performance, technology, application fields and development trends of the layer-4 switch.

What is layer-4 switch?

To understand the layer-4 switch, you must first understand the basic working principle and performance of the traditional layer-2 switch and the currently widely used layer-3 switch, only then can you identify the layer-4 switch. As we all know, the second layer switch performs end-to-end data exchange based on the MAC address of the second layer data link layer and the route selection through the station table. Because the establishment and maintenance of the station table is automatically completed by the switch, and the router is a layer-3 device, the addressing process is based on IP address addressing and generated through the route table and routing protocol.

Therefore, the biggest advantage of the second-layer switch is that the data transmission speed is fast, because it only needs to identify the MAC address in the data frame, and the algorithm for directly generating the forwarding Port Based on the MAC address is very simple, it is easy to use ASIC dedicated chips. Obviously, the second-layer switch solution is actually a cheap solution of "switch everywhere". Although this solution can also divide subnets, restrict broadcasting, and establish VLANs, however, it has little control capability and is not flexible enough, and cannot control the traffic of various information points. It lacks generic and convenient routing functions.

The layer-3 Switch directly performs end-to-end data exchange based on the layer-3 network layer IP address. On the surface, layer-3 switches are the combination of layer-2 switches and routers. However, this combination is not a simple physical combination, but a logical combination of strengths. When the first data stream of a certain information source performs layer-3 switching, the routing system generates a MAC ing table between the MAC address and IP address, the table is stored. When subsequent data streams from the same information source enter the switching environment again, the switch will map the table based on the address generated and saved for the first time, the second layer is directly transmitted from the source address to the destination address, which is no longer processed by the third route system. This eliminates the network delay caused by Route Selection and improves the packet forwarding efficiency, this solves the speed bottleneck caused by routes when inter-network information is transmitted. Therefore, the layer-3 switch can complete both the port switching function of the layer-2 switch and the routing function of some routers. That is, the switch solution of the layer-3 switch is actually a solution that supports multi-layer dynamic integration, although this multi-layer dynamic integration function can also be carried out by traditional routers and second-layer switches to some extent, compared with the three-layer switch, not only does it require more device configurations, more space, more wiring, and higher costs, but also significantly lower data transmission performance, because in massive data transmission, the router in the carrying solution cannot overcome the bottleneck of the route transmission rate.

Apparently, both layer-2 and layer-3 switches are end-to-end exchange processes based on port addresses. Although this vswitch technology is based on MAC addresses and IP addresses, it can greatly improve the data transmission rate between nodes, but cannot determine or dynamically limit the port exchange process and data traffic according to the application requirements of the port host, that is, there is a lack of layer-4 intelligent application exchange requirements. The layer-4 switch not only performs end-to-end switching, but also determines or limits the switching 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, as a result, it does not work on the transmission layer, but still performs exchange operations on the third layer, but is more sensitive to the third layer exchange. It fundamentally denies the key technology and role of the fourth layer exchange. We know that the layer-2 802.1p field of the data packet or the layer-3 IP ToS 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.