Overview of basic LAN switch knowledge

There are many areas worth learning about LAN switches. Here we mainly introduce the development of LAN multi-layer switching technology and applications. In the past few years, the network has undergone fundamental changes: the bridge has withdrawn from the historical stage, and there are fewer and fewer shared Ethernet networks in the LAN network. People's requirements for networks have led to the birth and development of a new generation of networks. The exchange technology is the core of the new network era.

The exchange technology has powerful addressing capabilities and excellent stability. It provides a solution for applications requiring high bandwidth and solves the problem of intelligent network, it greatly promotes the development of networks. There is no doubt that LAN switching has become an important technology and is widely used today.
 
LAN switching technology Overview
 
The purpose of switching in LAN networks is to improve network performance and reduce network congestion. At the same time, switching technology can speed up data movement, this greatly reduces the possibility of conflict due to the use of CSMA/CD protocols in Traditional Ethernet, thus eliminating network bottlenecks to a certain extent. The internal function of a LAN switch is similar to that of a bridge. It tracks the source address of the frame sent from each port and checks the destination address of the frame to select a route. The number of addresses that each port of a LAN switch can store determines the number of workstations it supports and the LAN segments that support many workstations. If each port of a vswitch supports only one address, it is equivalent to a port switching device. If each port supports multiple addresses, it is equivalent to a segment switching device. In addition to the switch method, LAN switches can also be divided into direct pass and storage forwarding ". After reading the target address of a frame, the LAN switch performs a cross-connection between the source port and the destination port. This type of switching has the minimum latency and wait time.

Correspondingly, the storage forwarding switch stores all frames in the memory and controls frame errors. If the cyclic redundancy check for a frame does not match, the frame is discarded. The storage and forwarding technology needs to move frames from a low-speed LAN to a high-speed LAN. Because all frames must be stored, this switching method will inevitably bring about a small latency. In addition, LAN switches can also support FDDI, fast Ethernet, ring-based network, Ethernet, and ATM. in a strict sense, ATM is not completely the second layer, increase the throughput of A vswitch. These multi-protocol LAN switches can transmit data from one L2 network to another. Figure 1 shows the LAN switch application. By connecting two servers to two separate ports, the LAN switch can provide two-way connections between the workstation and the server.
　
Generally, LAN switches can be divided into two types: backbone switches and workgroup switches. The backbone network switch backbone switch is a high-end switch used by the core network. The data it receives comes from the Hub and workgroup switches, which provide interconnection between these devices. A backbone network switch can usually be inserted with various network tabs. These cards support the following network types: FDDI, Ethernet, fast Ethernet, starting ring network, and ATM. Backbone Network switches are usually connected to one or more high-speed networks. A workgroup switch is a low-end device that connects multiple shared CIDR blocks through the sharing technology. A workgroup switch is usually used to connect to a PC or a low-traffic database server. An Ethernet switch with 12 ports is a typical switch. It provides 1.2 Gbit/s bandwidth and can be considered as 12 isolated Ethernet segments. Generally, the workgroup switch must be connected to a high-speed backbone network such as FDDI or fast Ethernet.
 
Working principle of layer-3 Switching Technology
 
Traditional routers need to process a large number of packages for each route. Because traditional routers support multiple protocols, they are implemented through software, therefore, software-based execution is slower than hardware-based, making routers a bottleneck in network performance. To solve the communication bottleneck of the router, layer-3 switching occurs. Layer-3 switching improves the performance of the router and provides higher intelligence for the network. Layer-3 switching is similar to a LAN switch, except that it forwards data based on IP addresses rather than MAC addresses.
 
Assume that two sites using the IP protocol communicate with each other through the layer-3 Switch: when sending Site A, the IP address of the destination site is known, however, you do not know the MAC address required to send messages on the LAN. Use address resolution ARP) to determine the MAC address of the target site. The sending station compares its own IP address with the IP address of the destination station, and uses the subnet mask configured in its software to extract the inner. If the destination site B and the sender Station A are in the same subnet, Site A broadcasts an ARP request, and site B returns its MAC address, station A caches the MAC address of Site B, encapsulates the package with the MAC address, and forwards the data, the second layer switch module finds the MAC address table and determines to send data packets to the destination port. If two sites are not in the same subnet, if Station A needs to communicate with Station C, station A must send an ARP encapsulation package to the "default path, the IP address of the "default path" has been set in the system software.

This IP address actually corresponds to the layer-3 Switch module of the layer-3 switch. Therefore, when station A broadcasts an ARP request to the IP address of the "default path", if the layer-3 switching module obtains the MAC address of the target Station C during the previous communication process, then, send A reply to the MAC address of the target Station C. Otherwise, the layer-3 Switch module broadcasts an ARP request to the target Station Based on the route information, the layer-3 Switch module replies to its MAC address. The layer-3 Switch module saves the address and replies to the sending Site. Later, when the packet forwarding between Site A and Site C is performed, the package will be encapsulated with the MAC address of the final destination site C, and the data forwarding process will all be handed over to the second layer for exchange processing, therefore, information is quickly exchanged.