The difference between three or four-layer exchange/four-layer Exchange technology Introduction

With the popularization of broadband, a variety of network applications in depth, our local area network is shouldering heavy traffic. Network system of audio, video, data and other information transmission is full of bandwidth consumption, we have to provide these data traffic differentiated services, so that the time delay sensitive and important data first pass, this has to consider the fourth layer Exchange to meet policy-based scheduling, QoS (Quality of Service: Quality of services and requirements for security services.

The difference between the exchange of two and three or four layers

The second layer Exchange realizes the fast information exchange between the hosts in the LAN, and the third layer Exchange is the perfect combination of the Exchange technology and the routing technology, while the fourth layer Exchange technology can provide the optimal allocation for the network application resources, realize the service quality, load balance and security control of the application service. Four-tier exchange is not to replace who, in fact, now the two-tier exchange and three-tier exchange has been integrated into four-layer switching technology.

The second layer switch completes the End-to-end data exchange based on the MAC address and MAC address Table of the second layer data link layer. The second layer switch only needs to identify the MAC address in the data frame, and forwards it directly according to the MAC address, so it is very convenient to use ASIC special chip to realize. The second layer of the Exchange solution, is a "Everywhere Exchange" scheme, although the scheme can be divided into subnets, limited broadcast, set up VLAN, but its control capacity is small, flexible enough, also unable to control traffic, lack of routing function.

The third layer switch is based on the third layer of network layer IP address to complete end-to-end data exchange, mainly applied to different VLAN subnet routing. When the first data flow of an information source is exchanged (routed) at the third level, the switch generates a map of the MAC address and IP address and stores the table as a subsequent stream of information sources enters the switch, and the switch will be based on the first generated and saved address mapping table, Directly from the second layer from the source address to the destination address, no longer through the third routing system processing, improve the efficiency of packet forwarding, to solve the VLAN subnet transmission of information between the traditional router generated speed bottleneck.

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, which can differentiate the application type of the packet according to the TCP/UDP port number to achieve the access control and service quality assurance of the application layer. You can view the contents of the third-tier data header source and destination addresses, and you can implement the key functions of bandwidth allocation, fault diagnosis, and access control to TCP/IP application Data flow based on observed information. The fourth layer switch optimizes the network through task assignment and load balance, and provides detailed traffic statistic information and accounting information, which solves the problems of network congestion, network security and network management at the application level, and makes the network intelligent and manageable.

Introduction to four-layer switching technology

The fourth layer of the OSI Network Reference Model is the transport layer. The transport layer is responsible for end-to-end communication, which is to coordinate communication between the network source and the target system. In the IP protocol stack, this is the protocol layer where TCP (Transmission Control Protocol) and UDP (User Datagram Protocol) reside. TCP and UDP contain port numbers, which can uniquely differentiate which application protocols each packet contains (such as HTTP, FTP, Telnet, and so on). The additional information provided by the TCP/UDP port number can be utilized by the network switch, which is used by the four-tier switch to differentiate the data in the packet, which is the basis of layer fourth exchange.

The main functions of the four-layer exchange are as follows: 1. Packet filtering: In traditional routers, the fourth-level information port number is used to define access control list filtering rules. Four-tier switching also borrows the concept of control lists, but unlike software-based routers, the fourth-tier switch is implemented in ASIC-specific high-speed chips, allowing the filter control to be carried out at wire speed.

2. Quality of service: TCP/UDP layer Fourth information can also be used to establish the priority of application communications. Layer fourth switching allows for prioritization based on port number (application), setting priority queues, ensuring that critical traffic (such as VOIP, video) is handled fastest, and that emergency applications get high level service from the network.

3. Load balancing: The fourth-tier switching load balancing principle is the exchange of virtual connections between IP addresses and TCP ports, sending packets directly to the corresponding ports of the destination computer. The switch with layer fourth switching capability can be used as a hardware load balancer to complete the load balancing of the server. Because layer fourth switching is based on hardware chips, performance is excellent, especially for the speed of network transmission, the speed of exchange far more than normal packet forwarding. Using layer fourth switch equipment, all cluster hosts through the fourth layer of switch and the external Internet connection, external customers to prevent the server through the fourth layer of switch dynamic allocation of servers to achieve dynamic load balancing, when one of the server fails, All traffic is dynamically allocated by the switch to other hosts in the cluster.