Communication Equipment-basic knowledge of bridges and switches

Bridges and switches are both data communication devices and work on the Layer 2 of the OSI reference model. Therefore, they are generally referred to as data link layer devices. They were first used in 1980s, at that time, it was mainly used to connect networks of the same type and forward data between networks. With the continuous development of network technology, today's bridges have been able to connect different types of networks, and their intelligence has also been improved.

Bridges used as network interconnection devices can be divided into several different types. The transparent bridge is mainly used in the Ethernet environment, and the source routing Bridge is mainly used in the licensing ring network, while the conversion bridge can usually be Ethernet and licensing ring in different network media types) data format and transmission protocol conversion.

Nowadays, switches have replaced traditional bridges and become the main network interconnection technology. Compared with bridges, vswitches provide better data throughput, higher port integration, lower cost per port, and more flexible and convenient to use.

Link Layer device Overview

The functions of bridges and switches are implemented at the data link layer. The role of the data link layer is to control data traffic, handle transmission errors, provide physical addresses without logical addresses), and manage access to physical media. By using different link layer protocols, bridges can implement all the above functions. Currently, more popular link layer protocols include Ethernet, licensing ring, and FDDI.

The implementation principle of the functions of bridges and switches is not complex. It mainly analyzes inbound data frames, makes forwarding decisions based on the information contained in the frames, and then forwards the data frames to the destination. The bridge forwards data frames in two forms. If the source path bridge technology is used, each data frame already contains the complete path to the destination. If the transparent bridge technology is used, then, each data frame is forwarded to the next node and finally to the destination.

Transparency to upper-layer protocols is an important advantage of bridges and switches. Because both devices work at the link layer, you do not need to check the information of the Upper-layer protocol. In this way, you can speed up data traffic forwarding using any network layer protocol. Generally, bridges support the following network protocols: AppleTalk, DECnet, TCP/IP, and XNS.

The bridge can filter data frames based on any domain established on the second layer. For example, we can set a bridge to reject all data frames from a specific network. Because the data link layer information contained in the data frame often marks the type of the Upper-layer protocol used, we can also use this as a parameter setting filter mechanism. In addition, effective filtering of data frames can greatly reduce unnecessary data traffic caused by broadcast or multi-point transmission.

What can I do if I use a bridge or a switch? The network type is divided into several small subnets to provide other functions. Because only a small amount of traffic needs to be forwarded after the subnet is divided, both the bridge and the switch can reduce the data traffic flowing through all the devices connected to the network segment. Bridges or switches can also act as firewalls to reduce possible network errors. Finally, bridges and switches can extend the valid connection range of the LAN and allow access to more remote devices.

From the above introduction, we can see that there are many similarities between bridges and switches, but there are still some significant differences between the two technologies. In terms of speed, the switch is significantly faster than the bridge, because the switch is mainly used for hardware exchange, while the bridge needs to use software for exchange. In addition, vswitches can connect networks with different bandwidths. For example, a 10 Mbps Ethernet LAN and a Mbps Ethernet LAN can be interconnected through a switch. In terms of switch technology, the switch supports open switch cut-through to reduce network latency, while the bridge can only use the storage and forwarding technology store-and-forward ). Finally, because the switch can provide dedicated bandwidth for each CIDR block, it can reduce the hit rate on the CIDR block.

Bridge Type　

Different types of bridges can be divided into multiple forms based on different features of the product. One of the more common ways is to divide bridges into local bridges and remote bridges. Local bridges are mainly used to provide direct connections between multiple LAN segments in the same geographic area. Remote bridges are used to connect LAN segments in different regions. Generally, telephone lines are used. The use of the two bridges is as follows:

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The remote bridge technology faces some challenges in implementing network interconnection, one of which is how to solve the speed difference between the LAN and WAN. Although some high-speed WAN technologies have been adopted, generally, the speed of LAN is much faster than that of Wan. This huge difference in the speed between the LAN and WAN makes it impossible for users to run applications with high latency requirements across the WAN.

Although remote switches cannot speed up the wide area network, they can compensate for the speed difference by providing sufficient buffering functions. For example, if a LAN device with a transmission rate of 3 Mbps wants to communicate with another device on the remote LAN, the bridge must adjust the data stream of 3 Mbps to avoid blocking WAN connections with only kbps of bandwidth. To solve this problem, the Bridge uses the internal cache to save the received data and then sends it to the wide area network at a rate that the wide area network can afford.

Vswitch type　

A switch and a bridge are also a data link layer device that can interconnect multiple physical network segments into a unified large network. Vswitches have many different types, including ATM switches, LAN switches, and wide area network switches.

ATM Switch　

An ATM switch can provide high-speed switching capability and scalable bandwidth for Working Groups, enterprise backbone networks, and WAN networks. The ATM switch supports voice, video, and data applications and is designed to exchange fixed-size information units, namely, ATM cells. It shows an enterprise network connected to multiple local networks through an ATM backbone.

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LAN switch

A lan switch can be used to connect multiple LAN segments and implement non-conflicting private communication between network devices. LAN switches can store and forward data frames at high speeds. It is a simple network that uses a LAN switch to connect 10-Mbps and 100-Mbps Ethernet.

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1. Basic knowledge: The difference between bridge and Internet Connection Sharing
2. How vswitches work and how they are classified