Basic knowledge of switches
The emergence of many new Client / Server applications and multimedia technologies has led to the traditional shared network far from meeting the requirements, which has promoted the emergence of LAN switches.
1. Definition of the switch The LAN switch has many ports, each port has its own dedicated bandwidth, and can be connected to different network segments. The communication between the various ports of the switch is simultaneous and parallel, which greatly improves the information throughput. To further improve performance, only one device can be connected to each port.
In order to realize the interconnection between switches or the connection with high-end servers, LAN switches generally have one or several high-speed ports, such as 100M Ethernet ports, FDDI ports or 155M ATM ports, thus ensuring the transmission performance of the entire network.
2. Features of the switch The users who share the LAN through the hub not only share the bandwidth, but also compete for bandwidth. Perhaps due to the need for more bandwidth by individual users, the available bandwidth of other users is relatively reduced, and even forced to wait, thus delaying communication and information processing. Using the network micro-segmentation technology of the switch, users of a large shared LAN can be divided into many independent network segments, reducing the number of users competing for bandwidth and increasing the available bandwidth of each user, thereby alleviating the congestion of the shared network. Because the switch can send information to the destination quickly and directly, it can greatly improve the speed and bandwidth, protect the user's previous investment in media, and provide good scalability. Therefore, the switch is not only an ideal replacement for the bridge It is an ideal substitute for the hub.
Compared with bridges and hubs, switches improve performance from the following aspects:
(1) By supporting parallel communication, the information throughput of the switch is improved.
(2) Divide the users on a traditional large local area network into several work groups, and connect one device or one work group to each port to effectively solve the crowding phenomenon. This method is called the network micro-segmentation (Micro-segmentaTIon) technology.
(3) The emergence of virtual network (VirtuaI LAN) technology brings greater flexibility to the use and management of switches. We will specifically introduce the virtual network later.
(4) The port density can be comparable to the hub. The general network system has one or several servers, and most of them are ordinary clients. Clients need to access the server, which causes the server's communication and transaction processing capabilities to become the key to the performance of the entire network.
The switch mainly improves the performance of the entire network by increasing the speed of the port connecting the server and the size of the corresponding frame buffer, so as to meet user requirements. Some high-end switches also use full-duplex technology to further increase the port bandwidth. The previous network equipment basically used half-duplex working mode, that is, when a host sends a data packet, it cannot receive the data packet, and when receiving the data packet, it cannot send the data packet. Due to the use of full-duplex technology, that is, the host can also receive data packets while sending data packets, the ordinary 10M port can become a 20M port, and the ordinary 100M port can become a 200M port, which further improves the information. Throughput.
3. Working principle of the switch The traditional switch is essentially a multi-port bridge with flow control capability, that is, a traditional (layer 2) switch. Introducing routing technology into switches can complete network layer routing, so it is called Layer 3 switching, which is a new development of switches. The working principle of the switch (Layer 2 switch) The switch is a networked device working at the link layer like a network bridge. Each port of it has a bridge function. Each port can be connected to a LAN or a high-performance website or server. Able to learn the connection of each port through self-learning. All ports are controlled by a dedicated processor and forward information through the control management bus.
At the same time, special network management software can be used for centralized management. In addition, in order to improve the speed and efficiency of data exchange, switches generally support multiple methods.
(1) Store and forward:
All conventional bridges use this method. Before sending data frames to other ports, they must store the received frames completely in the internal memory and send them to other ports after checking them, so that the delay is equal to the time and processing of receiving a complete data frame The sum of time. If the cascade is very long, it will cause serious performance problems, but this method can filter out the wrong data frames.
(2) Cut-in method:
This method only checks the target address of the data frame, which allows the data frame to be transmitted almost immediately, thereby greatly reducing the delay.
The disadvantage is that error frames will also be transmitted. When the probability of erroneous frames is small, the cut-in method can be used to increase the transmission speed. When the probability of erroneous frames is large, the store-and-forward method can be used to reduce the retransmission of erroneous frames.
4. Configuration of the switch We take the Catlystl900 switch from Cisco as an example to introduce the general configuration process of the switch.
For a new Catlystl900 switch, using its default configuration will work. This is because it is a hardware device that installs software in FlashMemory. When power is turned on, it first performs a series of self-tests. After testing all ports, the switch is in working condition. At this time, its exchange table is empty. It can learn the connection of each port through self-learning, and record the MAC address of the device in the exchange table. When there is information exchange, the switch performs data according to the exchange table Forward.
But in order to facilitate network management, Catlystl900 switch has a MAC address itself, so that it can be assigned an IP address and mask code. The network administrator must connect a terminal or emulation terminal through the serial port of the switch to assign an IP address to it. The default value is 0.0.0.0. After specifying the IP address, the network administrator can remotely manage through the network. The configuration interface of the Catlystl900 switch is in the form of a menu. In the default configuration, all its ports belong to the same VLAN, and in many cases, no modification is required.
(1) Connect the serial port of the computer to the Console port of the Catalyst1900 through an RS-232 cable, and run the emulation terminal software. After the Catalyst 1900 starts.
(2) After entering, enter the main menu:
(3) Press the "S" key to enter the system configuration menu: (configuration system name, location, date)
(4) Press the "N" key in the main menu to enter the network management menu (5) Configure the IP location (6) Configure the SNMP parameters
5. Types of switches Switches are data link layer devices, which can connect multiple physical LAN segments to a large network. Similar to the network, switch transmission and overflow are also based on MAC address transmission. Since the switch is implemented in hardware, the transmission speed is very fast. When transmitting data packets, the switch either uses the store-to-forward switching method or the off-to-through switching method. There are many types of switches, including ATM switches, LAN switches and different types of WAN switches.
ATM switch ATM (Asynchronous Transfer Mode) switch provides high-speed exchange of information and scalable bandwidth for workgroups, enterprise network hubs, and many other fields. ATM switches support voice, video and text data applications, and can be used to exchange fixed-length information units (sometimes called elements). The enterprise network is formed by connecting multiple LANs through ATM hub links.
LAN switch LAN switch is used for interconnection of multiple LAN segments. It carries out dedicated conflict-free communication between network devices and supports dialogue between multiple devices. LAN switches are mainly used to exchange data frames at high speed. Interconnect a 0Mbps Ethernet with a 100Mbps Ethernet through a LAN switch.
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