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In the past few years, the network has undergone a fundamental change: bridges have withdrawn from the historical stage, and shared Ethernet is becoming fewer and fewer in LAN networks. 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 network 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.
Architecture of layer-3 Exchange Technology
A layer-3 switch is also called a route switch. A layer-3 switch can be considered as a model. It involves the layer-2 and layer-3 of the ISO Reference Model. As a switch, it has the same attributes as the second layer, and combines the advantages of the second layer switch and the third layer router into a flexible solution, it can provide line rate performance at all levels, so it has certain routing performance. This integration structure also introduces policy management attributes, which not only associate Layer 2 with Layer 3, it also provides prioritized communication traffic processing, security, and a variety of other flexible functions, such as dynamic deployment of trunking, VPN and Intranet. Figure 2 lists the components of the layer-3 switch.
The interface layer includes all important LAN interfaces: 10/100 Mbit/s Ethernet, gibit Ethernet, FDDI, and ATM. The switching layer integrates multiple LAN interfaces and is supplemented by policy management. It also provides trunking, VLAN, and tag mechanisms. The routing layer provides the main LAN routing protocols: IP, IPX, and AppleT, and provides traditional routing or pass-through layer-3 forwarding technology through policy management. Policy management and administrative management enable the network administrator to adjust the network according to the specific needs of the enterprise or department. Compared with Layer 3, the level of adoption of Layer 2 determines the so-called network control classification, as shown in 3. A pure second-level solution, that is, the "Everywhere transformation" shown in the figure, which provides at least control over subnet division and broadcast restrictions. Layer-3 switches provide dynamic and integrated support for all levels in the classification. Traditional general-purpose routers and external switches can also achieve this goal, but compared with this solution, layer-3 switches only require less configuration, less wiring, and cheaper prices, and provides higher network performance.
Evolution of layer-3 Exchange Technology
With the continuous upgrade of hardware and software, the development of layer-3 switching technology has also undergone a "three generations" change. The first generation switch is a mixture of discrete electronic components and primitive software frameworks. The software function runs on a processing machine with fixed memory. With the improvement of management support and protocol functions, software functions are also increasing. When your daily business is more dependent on the network and the traffic on the network increases, the network device becomes a bottleneck. Although processors and memory become faster and more effective, the increase in communication traffic is more rapid. The first step to solve the problem is to simplify the network layer: replace vrouters with vswitches to reduce the overhead of data packets and significantly increase the transaction processing speed. Introduces a dedicated Integrated Circuit ASIC dedicated for optimizing Layer 2 processing. This improves the performance by 10 times and reduces the overall cost of the system. Figure 4 shows the first generation of architecture.
The third-generation exchange technology is not only based on the progress of the second generation, but also based on ASIC + RISC technology, which is an optional policy for layer-3 routing, multicast, and users) in terms of line rate performance, the total data throughput can exceed several million packets per second. Because a policy-based service mechanism is used to support QOS, the FIRE can be used to introduce distributed data packets to process DDP.) data packets can be quickly and independently transmitted to the system, at the same time, dynamic classification of PACE technology and RSVP are used to flexibly combine the performance of Layer 2 and Layer 3. In the layer-3 switch, you can use a built-in processor to support ASIC. For example, you do not need to upgrade hardware or sacrifice system performance. Layer-3 switches of the third generation support multimedia network communication, which can effectively reduce latency and ensure security. As switches, hubs, and NICs adopt a unified system environment, the vswitch supports image transmission over Ethernet. Figure 5 shows the architecture of the second and third generations.
Multi-layer exchange development prospects
With the development of LAN switching technology, layer-4 switching has emerged. It expands layer-3 and layer-2 switching, supports more fine-grained network adjustment, and gives priority to communication streams. The layer-4 switch is a policy-based route. It is located on the layer-4 of the ISO Reference Model and uses the layer-4 information. According to the layer-4 Information, for example, the port number of the data packet in TCP/UDP is exchanged. It allows you to prioritize communication data based on applications and use a certain amount of bandwidth for important applications based on the traffic of a specific application. In a sense, layer-4 Switching provides a service level COS in the network. This can reduce WWW or FTP traffic for an Intranet and set higher priority for E-MAIL or Telent traffic. Third, layer-4 switching is a process based on accelerated routing. Currently, stream or label-based routing technologies have also been released, for example, the Fast IP address and NHRP switch launched by 3Com and the MPLS Multi-Protocol Label Switch launched by Alcatel. Multi-layer switching helps bridge the LAN and WAN. With the development of information globalization, the boundaries between the LAN and WAN become increasingly blurred, multi-layer exchange technology lays a solid foundation for future scalable solutions.
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