Analyze how server switches work

What is the difference between a server switch and a common switch and a smart switch? I believe this is a headache for many users. I don't know what type of switch to choose. This article will solve your problem.

In the layer-4 switch, a virtual IP address (VIP) is set up for each server group for search. Each group of servers supports an application. Each application server address stored in the Domain Name Server (DNS) is a VIP address, rather than 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. Replace the VIP address in the terminal address with the actual Server IP address, and send the connection request to the server. In this way, all packets in the same range are mapped by the server switch and transmitted between the user and the same server.

Principle of layer-4 Switching

The fourth layer of the OSI model is the transport layer. The transport layer is responsible for peer communication, that is, coordinated communication between the network source and the target system. In the IP protocol stack, This is the protocol layer of TCP (a Transport Protocol) and UDP (user data packet protocol. In layer-4, the TCP and UDP headers contain port numbers, which uniquely differentiate which application protocols (such as HTTP and FTP) are contained in each packet ).

The endpoint system uses this information to distinguish packet data, especially the port number, so that a computer system at the receiving end can determine the type of the IP packet it receives and hand it over to appropriate high-level software. A combination of port numbers and device IP addresses is usually called "socket )". The port numbers between 1 and 255 are retained. They are called "well-known" ports, that is, these ports are the same in all TCP/I P protocol stack implementations of the host.

In addition to the "well-known" port, standard UNIX services are allocated between port 256 and port 1024. custom applications generally allocate port numbers over port 1024. You can find the latest list of allocated port Numbers on RFC1700 "Assigned Numbers. The additional information provided by the TCP/UDP port number can be used by the network switch, which is the basis for layer-4 switching. A vswitch with the layer-4 function can act as the "virtual IP" (VIP) frontend connected to the server.

Each server and server group supporting a single or common application is configured with a VIP address. This VIP address is sent and registered on the domain name system. When a service request is sent, the layer-4 switch identifies the start of a session by determining the start of TCP.

Then it uses complex algorithms to determine the best server for processing this request. Once this decision is made, the switch associates the session with a specific IP address and replaces the VIP address on the server with the real IP address of the server.

Each layer-4 switch stores a source IP address that matches the selected server and a connection table associated with the source TCP port. The layer-4 switch then forwards the connection request to the server. All subsequent packets are reinjected and forwarded between the client and the server until the switch discovers a session. When layer-4 switching is used.

Access can be connected with real servers to meet user-defined rules, such as enabling equal access to each server or allocating transmission streams based on the capacity of different servers. How to choose a layer-4 Switch

(1) Speed

To be effective in Enterprise Networks, layer-4 switching must provide comparable performance with layer-3 line rate routers. That is to say, layer-4 switching must operate on all ports at full-media speed, even on multiple Gigabit Ethernet connections. The Gigabit Ethernet speed is equal to the maximum speed of 1488000 packets per second (assuming the worst case, that is, all packets are the minimum size defined by the network and are 64 bytes long ).

(2) server capacity balancing algorithm

Based on the desired capacity balancing interval, there are many algorithms for layer-4 switches to allocate applications to servers, there are simple detection loop recent connections, detection loop latency, or detection server closed loop feedback. Among all predictions, closed-loop feedback provides the most accurate detection that reflects the current business volume of the server.

(3) Table capacity

It should be noted that the switch for layer-4 Switching requires the ability to differentiate and store a large number of sending table items. This is especially true for vswitches at the core of a CEN instance. The size of many second/third-layer switches tends to be proportional to the number of network devices. For a layer-4 switch, this quantity must be multiplied by the number of different application protocols and Sessions used in the network.

Therefore, the size of the table to be sent increases rapidly as the number of device and application types increases. Layer-4 switch designers need to consider this growth when designing their products. Large table capacity is critical to manufacturing high-performance switches that support line rate transmission of layer-4 traffic.

(4) Redundancy

The layer-4 server switch supports the redundant topology. When there is a dual-link network card with fault tolerance connection, it is possible to establish a completely redundant system from a server to the network card, the link and the server switch. Network Management switches can be managed through the following channels: Through RS-232 serial port (or parallel port) management, through Web browser management and through network management software management.

A serial port cable is attached to a network management switch for management. First, insert one end of the serial port cable into the serial port on the back of the switch, and the other end into the serial port of the general computer. Connect the vswitch to the computer. "Super Terminal" programs are provided in Windows 98 and Windows 2000. Open "Super Terminal" and set the connection parameters.

You can use the serial port cable to interact with the switch. This method does not occupy the bandwidth of the switch. Therefore, it is called "Out of band ). In this mode, the switch provides a menu-driven console interface or command line interface. You can use the "Tab" key or the arrow keys to move the menu and sub-menu.

Press the Enter key to run the corresponding command, or use a dedicated server switch to manage the switch. The command sets of vswitches of different brands are different. Even vswitches of the same brand have different commands. It is more convenient to use menu commands.

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