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Collection of knowledge on local network


A local area network (LAN) is a group of computers that is made up of multiple computers connected to each other in a defined area. Usually within a radius of several kilometers. Functions such as file management, application software sharing, printer sharing, workgroup scheduling, e-mail and fax services can be implemented on LAN. The local network is closed and can consist of two computers in an office or thousands of computers in a company. The following is latest essay on LAN knowledge model compiled by editor. Welcome to learn from it.

Essay on latest LAN knowledge model (1)

What is a local area network? A so-called local area network (LAN) is used to connect various computers, terminals and external devices in a limited area (for example, in a laboratory, office building or campus) into a single network. net . How to build a company's local network?

First of all, let's understand methods of building a network of enterprises of different sizes.

Create a corporate network with less than 10 people

Smaller companies with fewer than 10 employees typically have low network application requirements. Due to small number of employees, in principle, there is no need to separate VLANs (virtual local area networks), so it is enough to select a few - port switch.

Businesses with 10 to 100 employees need routing and subnetting

For these kinds of needs, a router + switch configuration is usually more appropriate. The router provides communication between internal network and external network and VLAN (virtual local area network) separation, as well as configuration of various firewalls and routing functions. One end of switch is connected to router as a subnet, and other end is connected to each terminal on subnet. To separate several subnets, it is enough to connect several switches from router. The group structure is shown in figure below: a popular LAN company usually chooses a tree topology (star topology extension) to form.

Tree topology has following advantages: 1. Ease of troubleshooting 2. Ease of network upgrades.

The difference between a router and a switch

1. The switch is basically designed to allow everyone to access Internet through a network cable, but each connects separately and uses their own broadband, so it does not affect everyone's Internet access even if other people download his. will not affect their own Internet access, and all computers using same switch are on same LAN.

2. The router has virtual dial-up function more than switch.Computers accessing Internet through same router use same broadband account. Other computers will obviously feel that Internet speed is very slow. Computers on same router are also on same local network.

Another example: difference between routers and switches

We know that router usually has 5 ports, one of which is WAN port, which is connected to broadband line, and other four ports are used to connect to computers on Internet, that is, router can support up to 4 computers to share Internet . What should we do if we want more computers to share same broadband line? Then we need to use switch at this time. A switch is different from a router. The switch usually has at least 8 ports. We only need to connect 1-4 ports in router. One of ports in switch connects a network cable to any port of switch, and other ports of switch can be connected to many computers to access Internet. So one network cable can be connected through a router combined with a switch to access Internet for more than 4 people. The role of switch here is equivalent to adding network cable ports, which can be understood as shunting becomes N ports.

Can a switch replace a router?

A router can be used as a switch, but a regular switch cannot be used as a router. The switch can connect multiple computers, and computers connected to switch have function of communicating with each other, forming an internal LAN, which can carry out company internal communication, and cannot access external network (that is, Internet). If you need Internet access, network support is also required, that is, one end of switch must be connected to router, router can realize switching function, and can also dial in to realize broadband connection, and allocate broadband access resources to switch, so that multiple computers can share Internet.

Warm Reminder: When router is used as a switch, IP address of router must be changed, otherwise IP address conflicts and everyone cannot access Internet, and DHCP function must be disabled. otherwise, computer cannot automatically obtain an IP address. Companies are not recommended to use a router as a switch, because even if routers do not conflict with each other and can access Internet normally, this will definitely affect network speed. This, in turn, affects efficiency of work, so for small and medium enterprises, router and switch are must-have network devices

How many computers cansupport router?

For wireless routers, it is claimed that wireless router can support 200 computers and a network cable. If it is only used for web browsing, dozens of computers can be connected without problems, but if there are several computers that boot at unlimited speed, then network is close to paralysis. As for actual wiring, a normal router usually has 5 ports, a WAN port is used to connect network cable, and remaining 4 ports, each port can only be connected to one computer. If many computers need to be connected to Internet, you need to use a switch. For enterprise routers, enterprises should consider number of routing ports when choosing a suitable router. There are many options in market, from a few ports to hundreds of ports. Users should choose according to their actual needs and future plans. There are many aspects to consider, such as expansion demand. Generally speaking, for small and medium enterprises, dozens of ports can usually meet needs of enterprises, what is really important is choice of number of ports for large enterprises. Make a forecast about possible future development of network, and then make a choice. From tens to hundreds of ports, you can choose wisely according to your needs.

How many cars can a switchboard carry?

The number of ports on a switch is most intuitive measure of a switch. This setting is typically used for switches with fixed ports. Common standard fixed port switches have 8, 12, 16, 24, and 48 ports. . Non-standard ports mainly include: 4 ports, 5 ports, 10 ports, 12 ports, 20 ports, 22 ports and 32 ports. Generally speaking, number of ports determines number of connections. Although a fixed port switch is relatively cheap, it can only provide limited ports and fixed interface types. Therefore, regardless of number of connected users or all certain restrictions in terms of available transmission media, but this type of switch widely used in workgroups and typically suited to small network and desktop switching environments.

Which switch is better?

For businesses with 100 to 500 employees, pay attention to internal network speed

To meet such demand, layer 3 switch + layer 2 switch solution is usually used. As core of network, layer 3 switch provides network configuration, separation and communication between VLANs, and each VLAN is formed by a layer 2 switch. To select trunk network equipment, it is recommended that backbone network equipment or base-level equipment choose high-performance backboneSwitches with layer 3 switching functions. If you want LAN backbone to have high reliability and availability, you should also consider redundancy and hot standby schemes of main switch. The type of network equipment at aggregation or access layer is usually a regular switch, performance and quantity of which is determined by number of computers connected to network and network topology.

2. Bandwidth Requirements

Generally speaking, Fast Ethernet should be sufficient for enterprise data traffic, and Gigabit Ethernet is required if there is a future option.

Summary: Regardless of whether an enterprise connects to Internet through a local area network, leased line or wireless access technology, there is always problem of accessing global network. At present, backbone network is not an obstacle to development of construction of broadband networks. Because backbone networks of various WANs mainly use fiber optic transmission technology and are generally referred to as high-speed transmission systems. The transfer speed of transmission line from central office to user is often very low, which is why we often say that construction of network access infrastructure is real "bottleneck" that limits construction of broadband networks, i.e. "one kilometer task". Therefore, it is necessary to understand and master current core network access technologies, intelligently select various network access schemes, and build a scientific, reasonable, practical and economical LAN communication system.

Three, built-in wiring design

EnterpriseIndustrial network laying should not only proceed from actual needs of enterprise itself, but also plan and design network according to enterprise cost estimate, at same time, it needs support of network equipment and servers, how to carry a reasonable network layout and wiring for computer rooms and office spaces, this is very important for network administrators. The basis for designing LAN wiring is distribution structure of network. At present, a company's network distribution map must be designed according to decorative drawings. The general principle is that it is best to place routers and switches in a relatively central location, and equipment with ventilation and cooling is also required. Before wiring, you must first understand location of desk in office, where can wires be cut and embedded, and where can wires not be buried? get on Internet?

The connection principle should take into account following considerations:

1. Practicality: adapt to needs of current and future development of enterprise with data transmission functions, image and voice communication

2. Flexibility: Any data point in wiring system can be easily connected to various types of equipment (such as telephones, computers, printers, faxes, etc.).

3. Scalability. The cable system is highly scalable, and expanded equipment can be easily connected to system as needed in future to implement various network services and applications.

4. Economical: The integrated wiring system is a kind of good initial investment characteristics, that is, it can maintain advanced nature of office without increasing new investment in next few years, and has an extremely high performance. -technological products with a low price-quality ratio. Under normal conditions, service life of integrated wiring system is 15 years.

Selecting a network cable

Cables are an important link connecting network access layer, aggregation layer, switching layer and network nodes. When wiring, it is best to use a dedicated conduit and not mix wiring with power lines, air conditioning lines, and other lines with radiation. At same time, you can choose CAT5E shielded twisted pair cable to maximize network performance.

Network planning and design

Placement of network equipment is best placed in central position of node, which not only saves embedded wiring costs, but also improves overall network performance and network transmission quality. Most modern network devices such as switches, routers, and hardware firewalls have a rack-mountable structure. All of them are housed in cabinets designed in accordance with international standards, which not only allows equipment to occupy a minimum of space, but also makes it easy to connect and manage other network equipment, and computer room will look neat and beautiful.

An enterprise's network diagram must consider equipment. Generally speaking, network equipment such as switches, routers, firewalls, encryption machines, etc., and network communication equipment such as optical transceivers, modems, etc., are placed in network cabinet, width of server cabinet is 19 inches, cabinet has removable retractable brackets according to U height. Users can flexibly adjust height according to height of their own servers to store servers, hubs, disk array cabinets and other equipment. Once a server is placed, all of its I/O cables exit back of cabinet and are evenly placed in cabinet's wire slot, and network cable labels are attached to facilitate efficient management in event of a failure. network failure.

In network diagram, each cabinet has a specificspace to facilitate expansion of network equipment and server equipment in future. The integrated wiring cabinet can accommodate telephone lines in addition to network wiring, so it is necessary to leave them in cabinet. Certain space. As far as cabinet is concerned, sufficient cable ducts must be provided so that network cables can enter and exit from top and bottom of cabinet. In addition, space occupied by cables is reduced so that installation, adjustment and maintenance of equipment does not interfere with wiring, and flow of heat-removing air is not blocked by cables; at same time, equipment wiring can be quickly detected in case of a malfunction.

Summary: Reasonable and perfect corporate network wiring not only has far-reaching implications for server maintenance in future, but also can reduce large-scale changes in layout structure, such as future upgrades and expansions, through efficient network wiring and facilitate network management. can maintain equipment and systems more efficiently. In addition, intelligent network and wiring of enterprise have more advantages in terms of heat dissipation in control room, which embodies concept of environmental protection and IT simplification.

Fourth, choice of network equipment

How to choose network equipment for small and medium businesses

Most of main network devices used by SMBs are nothing more than routers and switches. First, let's briefly describe differences between routers and switches. From a technical point of view, switch operates at link layer of network, and its main function is data packets; its working principle can be described in one sentence, that is, according to source address and destination address in data frame, mapping is established, path is established, and sending is completed. The router is relatively more complex. It works at network layer, and its main function is to connect different networks (such as LAN and WAN), implement interconnection between networks, and use IP addressing technology to find best path and complete delivery. As for three-layer switch, we often say that it is a switch with a specific "routing" function. In short, switch is faster, router is slower, switch configuration is simpler, router configuration is more complex, switch has fewer functions, and router has more functions, switch is MAC-based, and router is IP-based. The core of a switch is "switching". As name suggests, only single layer networks can be qualified for switching, while routers focus on "routing".

Choose your network equipment according to your actual needs

First, determine if your company needs to connect to different networks, for example, if it needs to connectyuchatsya to an external network and a local area network? Are there any complex network setup requirements? If yes, then router is one of best choice.

Is your router connected to a wired or wireless network?

In terms of geographic location and environmental factors, wired routers are more stable and have a stronger signal than wireless routers. Wired routers usually use RJ45 twisted pair cables to connect terminal devices, while wireless routers use wireless signals to connect terminals. The reason why wireless routers are not as stable as wired routers is that wireless routers are too dependent on from external factors such as space. ., environment will cause wireless signal to weaken, and biggest disadvantage of wired router is that it cannot exceed a certain length, while wireless router can usually reach a radiation range of 300 meters in open areas, but disadvantage is that there is a danger of fraying network, of course, if it is simple. A switch is enough to create a small internal local network.

Difference between enterprise routers and home routers

Some companies choose home routers when deploying wireless networks, which leads to very unstable wireless networks within company, affecting efficiency and greatly reducing. home routers are often designed according to home use environment. If it is applied in an enterprise, it is difficult to guarantee stability and security. Therefore, if an enterprise wants to provide wireless coverage, it must choose an enterprise-grade professional router. Compared to home routers, enterprise grade routers have higher performance in this regard and can satisfy more people with high speed internet access. Most enterprise-level routers use high-frequency network processors, which have strong processing capabilities, long transmission distances and large coverage areas, which can greatly improve network speed and bandwidth. The performance is also very stable and better. satisfy high-speed Internet needs of several people in enterprises. Due to lack of various protocols, home routers generally do not support protection against internal/external attacks, do not protect against viruses, Trojan horses and hackers, and it is difficult for enterprises to provide multiple protections. Compared with home routers, enterprise routers are more professional and sophisticated in industrial design, can support long-term uninterrupteduse and are more suitable for enterprise application environments. Therefore, for enterprises, when deploying wireless coverage, they should choose enterprise-grade professional routers. If they choose home routers for cost-saving purposes, it will definitely affect security and stability of network, resulting in large losses.

Essay on latest LAN knowledge model (2)

Ways to check if they belong to same local network:

Simple and clear method:

Open Network Neighborhood, check workgroup computer to see if you can see computer name of other party in it. Then two computers belong to same local network.

If they are connected to same switch or router and both have access to Internet, then it must be on same LAN.

Use LAN Viewer to verify that displayed computers are on same LAN.

Estimation method for same network segment:

Judging by IP address, they belong to same network segment and are located on same local network.

For example:

This is same network segment

A.A.A.X., three A's must match and X's must be different.

Examination method:

Convert IP addresses and subnet masks of two computers to binary numbers, and then AND corresponding bits, and results are same (the results are easier to judge after converting results to decimal numbers). , which means they belong to same subnet. The AND phase operation is that result of two conditions is simultaneously equal to 1, and result is equal to 1, otherwise it is equal to 0 (1 and 1=1, 1 and 0=0, 0 and 0=0).

Phase AND operation example:

The specific computer's IP address is and subnet mask is

Convert to binary: 11000000.00000001.00000001.00000100

Convert to binary: 11111111.11111111.11111111.11000000

Phase AND operation result: 11000000.00000001.00000001.00000000

Convert result to decimal:

Essay on latest LAN knowledge model (3)

1. Why use multiple WAN ports

A router with multiple wan ports usually has 2 wan ports, namely wan1 and wan2. Of course, there are more wan ports.

Why do we need multiple WAN ports?

A router is used to interconnect multiple broadband connections for three main reasons:

Increased bandwidth. Internet hosts can access Internet through any broadband network, which is equivalent to higher bandwidth in terms of applications.

Backup backup: if one of broadband links fails, you can use another broadbandaccess to access Internet to ensure smooth and uninterrupted operation of network.

ISP route selection: so-called "China Unicom access through China Unicom, China Telecom access through China Telecom", so purpose of visit is on right track.

At same time, a router with two wan ports can load balance and reduce latency.

2. Bandwidth overlay

Usually there can be two bandwidths at home, China Unicom or China Mobile, they can be charged for airtime, but network speed is not good, so it's not a pity, it's not good to use it, so what should I do? It can be used at this time Multiple WAN ports router.

1. Connect two bandwidths to WAN1 and WAN2 ports at same time.

For two wan ports, you can set corresponding WAN port network parameters.

After successful adjustment, two bandwidths can be superimposed.

2. Can bandwidth be imposed in all cases?

Answer: Consider from two points of view:

[1] For entire LAN, outgoing bandwidth is increased, which is equivalent to an increase in total bandwidth, which may have a superimposed effect.

[2] For a particular host, ability to overlay multiple broadband networks depends on host application.

Aside from bandwidth used by other hosts, what is Internet bandwidth for intranet host A?


The maximum download speed from host to server on external network is 12.5 MB/s (100 Mbps) or 2.5 MB/s (20 Mbps). The reason is that when booting to same server, only a specific WAN port can be used. For example, QQ downloads email attachments, downloads Baidu network drive, etc. If it is a multi-channel download, download speed may be superimposed.


If download is enabled on Xunlei and multiple resources are downloaded at same time, total bandwidth can reach 120M, that is, bandwidth of WAN port can overlap. P2P video, etc.