Load balancing based on layer fourth switching technology

This paper introduces the concept of layer fourth switching technology, the technical principle and how to use the fourth layer Exchange technology to realize the load balance of application server in the distance education system.

　　1 Introduction

Today's world has entered the information age, with the rapid development of society and the increasing demand for network applications, the network speed and bandwidth requirements continue to rise. It is in this development situation, many high-speed exchange of new technologies continue to emerge. 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, and the fourth layer Exchange technology described in detail below can provide the optimal allocation for the network application resources and realize the load balance of the application service.

　　2 Layer Fourth Exchange technology

2.1 Brief Introduction

A simple definition of layer fourth exchange is that it is a function that determines that the transmission is based not only on the MAC address (the second Layer Bridge) or the source/destination IP address (third-tier routing), but also on the TCP/UDP (layer fourth) application port number. Layer Fourth switching functions are like virtual IP, pointing to the physical server. It transmits a variety of business compliance protocols, with HTTP, FTP, NFS, Telnet, or other protocols. These services require a complex load balancing algorithm based on the physical server. In the IP world, the business type is determined by the terminal TCP or UDP port address, and the application interval in layer fourth switching is determined by the source and terminal IP addresses, TCP, and UDP ports.

A virtual IP address (VIP) is set up for each server group for search in layer fourth exchange, and each group of servers supports some application. 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 TCP SYN 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 passes the connection request to the server. In this way, all packets in the same interval are mapped by the server switch and transmitted between the user and the same server.

2.2 Technical principle

The fourth layer of the OSI 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.

In layer fourth, TCP and UDP headers contain port numbers, which can uniquely differentiate which application protocols each packet contains (for example, HTTP, FTP, and so on). The endpoint system uses this information to differentiate the data in the packet, especially the port number, which enables a receiving computer to determine the type of IP packet it receives and hand it over to the appropriate high-level software. The combination of port number and device IP address is often referred to as "socket". The most recent list of allocation port numbers can be found on the RFC 1700 "Assigned Numbers".

The additional information provided by the TCP/UDP port number can be used by the network switch, which is the basis of layer fourth exchange. A switch with layer fourth functionality can function as a front-end to the "Virtual IP" (VIP) connected to the server. Each server and server group that supports a single or universal application is configured with a VIP address. This VIP address is sent out and registered on the domain Name System.

When a service request is issued, layer fourth switches to identify the start of a session by determining TCP start. It then uses complex algorithms to determine the best server to process the request. Once this decision is made, the switch links the session to a specific IP address and replaces the VIP address on the server with the server's real IP address.

Each layer fourth switch holds a connection table that matches the selected server's source IP address and the source TCP port. Then layer fourth switches forward the connection request to this server. All subsequent packets are again mapped and forwarded between the client and the server until the switch discovers the session.

In the case of layer fourth exchange, access can be connected to a real server to meet user-established rules, such as having an equal number of accesses per server or allocating transport flows based on the capacity of different servers.

2.3 Products with fourth-tier exchange capability

At present, Berkeley Networks Company, Alteon Networks Company and other companies have a relatively mature fourth-tier exchange products and modules launched. Berkeley Networks's exponent E4 and Alteon Networks 1802 fourth tier Exchange products have outstanding performance and flexibility to make smarter forwarding decisions than the second and third tier switches. Because the code of Baotou query is embedded into the special integrated circuit (ASIC) in the switch, it will hardly cause any delay. These two vendors ' switches are capable of 10M, 100M, and Gigabit Ethernet, but Berkeley switches are designed for enterprise applications, while Alteon switches are for organizations that have a large number of Web or FTP servers. The fourth layer switching technology of Alteon can be used to monitor the performance and operation of the server, and to allocate the data traffic to the appropriate server in a cost-effective manner according to the health status of different servers. At the same time, the layer fourth switching technology of Alteon has a Web cache redirection feature that intercepts HTTP traffic destined for remote Internet hosts and redirects them to a local cache server, which greatly speeds up access to the Internet, And save a lot of valuable WAN bandwidth. And this is completely transparent to both the user and the information provider and does not require any user or information provider to make any settings.

SmartSwitch Router and torrent networking Technologies, a Cabletron company, is also a fourth-tier exchange product with IP9000 Gigabit Router. The SmartSwitch router can realize the upgrading of backbone network from conventional third layer to comprehensive third-layer, fourth-layer switching function, its unique WAN integration capability and the access control based on layer fourth exchange have played a key role in secure and orderly network data transmission. In addition, Cabletron SmartSwitch router provides different levels of prioritization for specific business application data exchange based on the QoS features of layer fourth switching.

　　3 Implementing server load Balancing using layer fourth switching technology

The following design comes from the practical application of the Network center of the Network Education Institute of a university. Through the Alteon layer fourth switch, the load balance of various application services is provided for distance teaching, and the overall performance of the network is improved.

Students use the Internet for Remote interactive learning. The Network Center of the Network Institute has made three sets of servers, each of which includes several servers with the same content. There are Web server groups, teaching server groups, data (database) server groups. Each set of server groups is configured with a virtual IP. Students access these application servers over the Internet. Each group of servers is connected to the Alteon layer fourth switch to implement load balancing of application services on the switch.

The Alteon layer fourth switch monitors the availability of the server, including physical connections, server hosts, and the health of the service application itself, and when a server is found unable to provide the appropriate service, the switch automatically assigns the application request to a good other server. Alteon layer Fourth switches can further ensure the reliability of the server system by setting the maximum number of sessions that each server can withstand, setting up overflow servers, and backup servers. The server uses a variety of load balancing algorithms for load balancing within the same LAN, including least Connection, Round Robin, Minmiss and hashing algorithms, and weighting of algorithms, and so on. When the server is not in the same LAN, the Globalload balance technology of Alteon switch is used to realize the rationality of load sharing.

Suppose the Web server group has three Web servers with the same content S1, S2, S3. Where S1 real IP is 10.1.1.1,S2 real IP is 10.1.1.2,S3 real IP is 10.1.1.3. The virtual IP for this Web server group is 61.134.38.5.

When multiple students visit our web service at the same time, the Alteon layer fourth switch accepts multiple concurrent requests to access Web services on 61.134.38.5. At this point, the Alteon layer fourth switch will allocate these requests reasonably to S1, S2 and S3 to realize dynamic load balancing according to some algorithms.

The above paper briefly introduces the application of layer fourth switching technology in server load balancing. However, the fourth-tier exchange supports other functions, such as the transport flow control based on the application type and the user ID, in addition to the load balancing function. Using multi-level queuing technology, layer fourth switches can label the transport flow and assign priority to the transport stream according to the application. In addition, layer fourth switches are placed directly on the front of the server to understand the application session content and user permissions, making it an ideal platform to prevent unauthorized access to the server.

　　4 Summary

With the development trend of network information system from small to medium-sized to large, switching technology also from the original MAC address Exchange, the development of IP address Exchange, further development to the ip+ port based exchange, now also proposed the seventh layer Exchange (content-based Exchange). In this paper, the fourth layer switching technology is introduced, and the technology is applied to the education system to realize the load balance of the server. It can be seen that the continuous development of network switching technology has changed from data based Exchange to an application based exchange, which not only improves the speed of network access, but also optimizes the overall performance of the network.