LAN classic fault resolution (essential post)

The biggest advantage of LAN is resource sharing, but in actual use, we often encounter such problems: the other party has obviously shared various resources, but they can not access them in the LAN. Since there are many possibilities for this kind of failure, it is difficult for newbies to find out where the failure is within a short period of time. Therefore, a comprehensive analysis of LAN failures is carried out in the form of examples.
1. Sheep lice appear on the sheep-the network card is not obedient [Fault phenomenon] A PCI network card can automatically install the driver under Windows, and the network protocol and related parameters have been correctly configured, but the network always appears when in use. When the time is bad, this problem still exists after replacing other network cards; and this network card is normal on other computers.
[Analysis and Solution] First, make sure that the driver of the network card is correct. It is best to use the driver provided with the network card, or download the corresponding driver to the driver home (http: //) according to the model of the network card. If there is no driver, you can try the installation according to the manufacturer of the main chip on the network card.
After the network card driver installation is complete, enter the "Control Panel → System" window, then you should see the currently installed network card under the "Device Manager", if there is a circled yellow "!" Icon in front of the network card, it means The network card has been installed in the system, but it conflicts with other hardware. At this time, there are two solutions: one is to delete or temporarily disable another device (such as a sound card) that conflicts with the network card, and then restart to try to solve the problem. If it can be solved, then reinstall the sound card driver or change the interrupt number of the sound card Make the two no longer conflict; another method is to delete the driver of the network card and then reinstall, if necessary, adjust the interrupt number occupied by the network card until the conflict no longer occurs.
If there is a resource conflict, the device that conflicts with the network card and the conflicting interrupt number or input and output address will be given in the "Conflict Device List" on the "Resources" tab, and then the resource allocation must be performed manually. For example, the interrupt address used by some early network cards is "3", which will conflict with the COM2 serial port. If your COM2 serial port is idle, you can turn it off in "Communication Port → Properties"; or in the CMOS settings, set " Onboard UART Port "is set to" Disable "to close the COM2 serial port, thus giving the interrupt address" 3 "to the network card. Some PCI network cards use the interrupt address "10", which conflicts with some graphics cards. You can set "Assign IRQ For VGA" to "Disable" in the BIOS without assigning a fixed interrupt to the graphics card.
[Alternative network card failure] In the device manager, you can see a yellow exclamation mark next to the network card model. Obviously the driver installation was unsuccessful, but the correct driver was installed N times. Guess what? Later it was found that the network card was loose.
2. The big environment is not good [Fault phenomenon] Computer connection and sharing in the local area network are normal. It is also normal to copy a few megabytes or tens of megabytes of files in this network, but once you copy hundreds of megabytes of files, it will The prompt "Insufficient network resources" appears, and then I can no longer find "My Network Places".
[Analysis and Solution] Since the computer connection and sharing are normal, it means that there is no problem with the network connection, network protocol and software settings. However, because a large amount of data needs to be read frequently, this requires a relatively stable transmission environment. If there is interference in the entire network line, this stable environment will be destroyed and a network failure will occur. However, network equipment such as hubs, routers, and switches are not very sensitive to external interference, so the largest interference may occur on the network card or network link.
For the network card, if the structure inside the chassis is relatively compact, installing the network card in the slot next to the graphics card, sound card and other cards may cause the electromagnetic waves between these cards to interfere with each other, resulting in the appearance of large files when copying Error message. The solution is to unplug the network card after turning off the computer and reinsert it in a slot farther away from the graphics card or sound card.
For network cables, it is recommended that you choose shielded cables, because they usually have shielded anti-interference layer protection to prevent external electromagnetic wave interference. Currently, the five types of cables on the market or super five types of cables are basically all It is a shielded cable. In addition, it is recommended that you do not place TVs, stereos, and other electrical appliances near computers, network cables, and hubs.
3. Ping you to Ping for thousands of times-unsuccessful [fault phenomenon] There are two computers in the local area network can be connected to other computers and use the resources of the other computer, but the two computers can not be pinged.
[Analysis and Solution] Since it can be connected to other computers, it means that there is no problem in network connection and network protocol, so it is mainly considered from the aspect of software attribute setting. Because the Ping program uses the ICMP protocol, most of these failures occur when the firewall software is installed on the opposite computer and the ICMP protocol is blocked. So you need to check the computer's firewall software settings to see if the ICMP protocol is blocked.

In addition, after the firewall attached to the system is activated in Windows XP, it will automatically block some commonly used network functions. For example, when the computer on the network uses the ping command to detect the network connection status, you will see the "Request TImed out" error message; but after selecting the "Allow incoming echo request" item under the "ICMP" tab, Run the ping command again to get normal feedback.
4. Can't see me and you [Fault Symptom] After opening "My Network Places", I can only view some computers, but I can't see some computers in the LAN, or even my own computer. What's wrong?
【Analysis and Solution】 Under the premise that the local area network is unblocked, whether it is not possible to view the machine or other computers on the network, it is due to the failure to install the file and print sharing service in the computer that cannot be viewed.
When installing file and print services, double-click the "Network" icon in the control panel, click the "Add" button in the pop-up window, select the "Services" item, and select "Microsoft Network Files" in the "Network Services" window Share with printer ". After completion, select "File and Print Sharing" in the "Network" property window, and then check the "Allow other users to access my files" check box. After installing the file and print sharing service, you need to restart the computer.
In addition, if the computer workgroup setting in the LAN is wrong, it may not be directly viewable in a workgroup. For example, the workgroup of most computers is set to "office", but the workgroup of several computers is set to "office1", so that when the "office" workgroup is opened, the computers in the "office1" workgroup cannot be viewed, so The name of the working group needs to be unified. When you change the workgroup name, you can click the "Identity" tab in the "Network" property window, and set the computer name and workgroup name respectively. In order to distinguish the computers in the local area network, it is recommended to name each computer according to the user's name.

Use "half search" method to narrow down the network fault

Step one half: Determine whether it is a hardware problem or a software problem. First, observe the color of the network card indicator when it is turned on: if it is green, it means the line is clear; if it is yellow, it means that the line is not connected Usually pay attention to observation). If the display fails, use a cable tester to test the network cable and check whether there is any problem with the network card. Under normal circumstances, the probability of network cable failure is high, and the probability of network card damage is small. If the hardware fault is eliminated, go to step two.
Step two in half: determine whether the problem with this machine is not Internet access is generally caused by the failure of this machine, sometimes it may be due to a problem with the switching equipment or proxy server on the campus network. The easy way to determine if there is a problem with this machine is to ask the network administrator and other colleagues whether they can go online. If it is judged as a local problem, go to step 3.
Step three in half: determine whether it is a security setting problem or a network card setting problem, execute the "ping" command, and if the data packet sent is answered (the return on the screen is "reply from 10.91.20.1:bytes=32 TIme <10ms ttl = 128" Class information>, the problem should be in the corresponding security settings of the machine. Of course, these security settings are not artificially changed in many cases, but caused by misoperation or viruses. In this case, if it is a Windows 98 system , Just reinstall IE; if it is a Windows 2000 system, you should also take a look at the IP security related settings to determine whether there is a port address shielding, etc. If you can access the Internet, but many websites can not go in, or the e-mail can not log in, you must It is because IE has been modified, and reinstalling IE can solve it. If there is no response after sending the data packet, the problem should be related to the settings of the local network card. If it is determined to be a problem related to the network card, please go to step 4.
Step 4: Determine whether there is a problem with the network card driver installation or the IP-related property settings are incorrect. Run the "ping 127.0.0.1" command to determine whether there is a response packet. If there is, and you can see yourself in the network neighborhood, the network card driver is generally no problem. The focus of the problem should be on the network card's IP attribute settings. If the computer in the LAN is set to "Obtain an IP address automatically", check the WINS configuration tab and note whether the "Use DHCP for WINS resolution" item is selected. If not, select it. If the TCP / IP setting of the computer in the local area network is "specified IP address", the focus of the check is on the IP address, subnet mask, DNS, gateway, and WINS related settings. These contents are related to the LAN configuration of the unit, please be flexible. If ping 127.0.0.1 does not respond, then there must be a problem with the network card driver installation. Reinstall and configure accordingly.
There is also a special case. You can ping yourself with the ping command, but your network neighbors ca n’t see any computers. There is no problem in checking the TCP / IP configuration, but you ca n’t go online. Most of these problems are caused by computer viruses, antivirus and reinstall the network card driver can solve the problem. The author has encountered several cases of this phenomenon, and all methods have been successfully resolved.
Because the specific configuration of different LANs is different, please deal with related issues flexibly.

Windows XP network failure easily check

Source: China Computer Education News Editor: ycx

[03-10-17 10:21] Author: Swiss Air

When the network fails, the first thing you think of is to enter some related commands in the command prompt, such as ping to diagnose? In fact, in Windows XP, you can use "Help and Support" to complete all network diagnosis easily and quickly!

Step 1 Click "Start → Help and Support" to open the "Help and Support Center" and check "Use tools to view your computer information and analyze problems".

Step 2 Select "Network Diagnostics" in the newly opened window. You can see that the right window has "Scan your system" and "Set Scan Options" options. In order to get complete and comprehensive network diagnostic information, we select "Set Scan Options", and select all the check boxes, then "Save Options", and then click "Scan Your System" (pictured).

Step 3 After waiting for more than ten seconds, a diagnostic report with various tests and detailed information collected is completed. This includes whether there is a network connection in your system, whether programs and services related to the network are running, and basic information about your computer.

How is your network fault found?

Calm the broadcast storm caused by the loop

The author is a webmaster. Recently, our local area network has been reformed, and all the network cables have been re-routed. The original network has 70 points, all of which are star-shaped structures. Now more than 30 users have been added, which means that only one switch needs to be added. The current network structure is like this: the entire network adopts a star topology, the central computer room is equipped with a TCL three-layer switch, and the server mainly provides FTP, file services, Web and other services. Each floor uses TCL switches, all with VLAN technology, and each terminal accesses the network through a 100M Avaya network cable. When the network was first used, all aspects were good, but recently the network has often dropped, and sometimes even simply went on strike. The leader will solve the problem in three days, or say goodbye to him. Ooo, Ooo, Ooo ... Fortunately, Kung Fu pays off, after three days and nights of hard work and meditation, I finally solved the problem. Now, my colleagues call me Huang Gong, and I am afraid that the wages will also rise sharply, ha ha ha ...

It is said that there are N users on and off in a certain year and month and day when they reflect the network connection, and sometimes the network neighbors cannot visit each other. Because the faulty users are distributed on multiple floors and the fault points are not concentrated, the impact is particularly bad. At first, I thought that the port of the switch was too large, and the switch and server were restarted N times, but it still didn't work. Yes, we quickly negotiated to start with the software, first remove the virus from the server, and then turn off each switch, to kill each machine, but the fault still exists. When pinging some servers or computers in the network, packets are still lost, and the network is intermittent.

God, I'm going crazy! Back home that night, I carefully recalled the failure of the day, and found that when I was disinfecting and disconnecting individual switches, the network returned to normal, and when I plugged it in again, I disconnected again. Thinking of this seems to have a little eyebrow. When I went to work the next day, I disconnected all the switches and plugged them in one by one until I found the one with the problem. After careful observation, I finally found the problem. It turned out that when this network was built at that time, two cascade cables were left between the core switch and the sub-switch, usually only one was inserted, and the other was spare. On the switch, both are plugged in. When a user on the switch sends a message to another user, the data packet will cyclically send the data packet through the core switch along another spare line. When the amount of information is large, the resources of the core switch will be wasted, causing the network speed to drop until disconnection.

The failure was mainly due to the existence of loops in the network, which caused each frame to be repeatedly broadcast in the network, causing a broadcast storm. To eliminate the network broadcast storm caused by this network loop connection, you can use the STP protocol. You can consult Cisco and other related books, so I won't say much here. In addition, when we do a relatively large network in the future, we must create detailed files, including network wiring diagrams, IP and MAC correspondence tables, etc., and set up digital tubes on the network line. The failure was verified by a new colleague who was careless.

IP and MAC binding problems

Q: My computer originally used a fixed IP address on the public network. In order to avoid being misappropriated by others, the "arp -s ip mac" command is used to bind the MAC address and the IP address. Later, for some reason, the "arp -d ip mac" command was used to cancel the binding. However, the strange thing is that after canceling the binding, the IP address cannot be used on other computers, but only on my own computer. It should be noted that my computer is not a proxy server.

Answer: Although in the TCP / IP network, the computer often needs to set the IP address to communicate, however, in fact, the communication between computers is not through the IP address, but through the MAC address of the network card. The IP address is only used to query the MAC address of the computer to be communicated with.

The ARP protocol is used to notify each other's computers and network equipment of the MAC address corresponding to their IP. The computer's ARP cache contains one or more tables for storing IP addresses and their resolved Ethernet MAC addresses. After a computer communicates with another computer with an IP address, the corresponding MAC address is retained in the ARP cache. Therefore, the next time you communicate with a computer with the same IP address, you will no longer query the MAC address, but directly reference the MAC address in the cache. In addition, it should be noted that items added through the "-s" parameter are static items and will not cause the ARP cache to time out. These items will be deleted only after the TCP / IP protocol is terminated and then started. Therefore, even if you cancel the binding, other computers will still think that you are using the original IP address within a short time.

In a switched network, the switch also maintains a MAC address table and sends data to the destination computer based on the MAC address. After binding the IP and MAC addresses, the switch will record the MAC address as long as it has communicated with the switch. In this way, even if someone later uses the same IP address, they will still not be able to communicate with the gateway, and will not be able to connect to the outside unless the switch is restarted, the MAC table is cleared, or the MAC address table exceeds the specified aging time

The local area network is a 10Mbps Ethernet connected by HUB. Why does the system prompt that only 800KB ~ 900KB / s is transmitted when transferring files.

This is because the rate is measured differently.

One is Bit? Bit ?, and the other is Byte? Byte ?. There are usually 8 Bits in 1 Byte. The network bandwidth is usually measured in bps (nominal bit / s), that is, "Bits-Per-Second (the number of bits per second, which is usually translated into baud rate)", and many of the download tool software measurement units It is Byte / s, so the difference between the two is 8 times.

Apart from the measurement method, the main reasons why the network cannot reach the nominal transmission rate include:

Hub limitations. The hub has a shared bandwidth of 10Mbps. If all ports are in communication, the transmission rate available for each port is about 0.625MB per second (calculation method is 10 ÷ 16). If you want to obtain a transmission rate close to the theoretical bandwidth, you must use a switch as a hub device.

The reason for the network card. If the quality of the network card is not good, there are often errors in the sent data packets, which cause the data packets to be retransmitted frequently, or more received data packets have errors, which will also reduce the speed of copying files.

The reason for the network cable. If the network cable is too long, the signal attenuation is relatively severe, or although the distance of the network cable is short, the quality of the network cable is not good, and it cannot reach the theoretical speed. In addition, when the network is busy, the ideal speed cannot be achieved.

20.
Question: Seven users are connected through the switch and are ready to use the routing function of the ADSL Modem to achieve Internet connection sharing. ISP provides a fixed IP address, and binds the MAC address of the network card, you can access the Internet after booting, instead of using virtual dialing. Excuse me, how should I configure this ADSL Modem to achieve Internet connection sharing?

Answer: If the ISP binds the IP address and the MAC address of the network card together, it is impossible to share the Internet through the routing function of the ADSL Modem. The reason is simple. Each network card has a unique MAC address, so other computers will be denied access to the Internet connection. The only solution is to connect the ADSL Modem to the computer where the ISP has bound the MAC address, and set the computer as a proxy server, and other computers as clients to achieve Internet connection sharing.

21. Question: How can I use a VPN to enable two LANs to access each other through the Internet? I have tried a dial-up machine with a modem that can be connected to the LAN using a VPN, but I only found the server, but I ca n’t see the other machines. Why? What?

Answer: First of all, it needs to be explained that the main function of VPN is for a client to remotely access the VPN server or access the network where the VPN server is located through the VPN server. Two LANs can access computers in each other's network through the Internet and can only do VPN routing.

If a remote client accesses the VPN server and its network, the VPN server needs to be configured correctly, mainly because the VPN server assigns an IP address to the remote client. When the VPN server and the DHCP server are not on the same computer, you can use DHCP to assign IP addresses to remote clients; when the VPN server and the DHCP server are on the same computer, you can only use the static address allocation method. Properties → IP tab ".

After dialing, the local area network cannot be accessed because there is no IP address assigned to a legitimate local area network. In addition, when using VPN dial-up, the dial-up end must have a legal IP address, otherwise dialing the VPN server is meaningless.

When setting up VPN routing to connect two LANs, both parties need to create a "demand dial interface" and create a routing table in the "routing and remote access → routing interface" of the VPN server.

If each VPN server has a legal IP address, you can create a static route (added in "IP routing → General routing"), if the VPN server does not have a legal IP address, you can use the RIP protocol to create a dynamic route (in the "IP Add "New Routing Protocol → RIP Version 2 for Internet Protocol" to Routing → General and configure it correctly.

When the VPN server does not have a legal IP address, problems will occur when the peer VPN server dials the local VPN server. At this time, you can use dynamic domain name resolution software on the VPN server without a legal IP address and apply for a domain name for this VPN server, and the peer VPN server can dial this domain name.

Gateway squeezes 80 ports

Q: The operating system of the server I set up is Windows 2000 Server Edition, and it has WWW, DNS, FTP (SERV-U), and E-mail (Web EasyMail) services. Specify the private IP address "172.16.108.a", specify the external network IP "218.106.98.b" through the exchange port, and bind the internal network IP "172.16.108.a", so that pointing to the domain name allows external users Access my server. However, port 80 of the web server is always inaccessible. Later, I added port 81 to the Web, and I can fully access the Web page through the port 81 of the external IP. Is it necessary to set up port mapping (the server adapter is a single RJ45 / 10Mbps LAN interface)? Will there be any problems with the gateway settings?

Answer: Judging from your question, it should be that your gateway occupies port 80, and "adding port 81 in the web, you can fully access the web page through port 81 of the external IP" means that you use 80 The port can be forwarded by the gateway, further indicating that the server has no problems. Generally, port mapping is not required.

To determine whether the server is faulty, you can use the replacement method:

â‘  Find another workstation, install only IIS (default installation), and install a network card (set to 172.16.108.a and correctly set the gateway), use this computer to temporarily replace your server, access 218.106.98.b on the Internet See if it is successful, if it can, it means that the fault is with you, otherwise the fault is at the gateway.

â‘¡Disconnect your computer from the network temporarily, install a Modem, dial-up Internet, and then enter ipconfig in the command window to view the external network address you obtained, let others access your dial-up Modem in IE IP address to see if it can be accessed, if it can indicate that your computer is not faulty; if not, it indicates that the fault is in the computer (if your IIS settings specify the address, please modify it to the correct address, that is, the address obtained after Modem dials ).

Permission issue of direct connection

Q: When two laptops with Windows XP system are directly connected using twisted pair, the connection is unstable, and the other computer often cannot browse, and even the workgroup cannot be opened, prompting "\\ computer name \ ShareDocs can not be accessed You may not have permission to use network resources. Please contact the administrator of this server to find out if you have access rights. You cannot access the network location. "What is the reason?

Answer: This must solve the problem of IP address and user permissions, there are several methods:

First, you can set a private IP address for each laptop. For example, one is 192.168.1.10, the other is 192.168.1.20, and the subnet mask is 255.255.255.0. Or both use the "automatically obtain IP address" method to make it automatically obtain the IP address of the "169.254.0.1 ~ 169.254.255.254" segment.

Second, enable the "Guest" account on each laptop. Run "Computer Management" from "Administrative Tools", select "Local Users and Groups-Users", right-click "Guest" in the right pane, select "Properties", in the "General" tab Cancel "Account is disabled."

Third, open "Explorer", select "Folder Properties" from the "Tools" menu, and cancel "Use Simple Folder Sharing (Recommended)" from "Files and Folders" in the "View" tab.

Fourth, open "Local Area Connection" and confirm that the Internet Connection Firewall is not enabled in the "Advanced" tab of the "Local Area Connection" property.

Fifth, click "Set up a home or small office network" in the "Network Connections" window, run the "Network Installation Wizard", and select "This computer belongs to a network without an Internet connection." Then, open Windows Explorer and set up a shared folder.

Analysis of Browsing between NETBIOS and Network Neighborhood

Questions about online neighbors have been asked a lot, and misunderstandings in understanding are generally more serious. In view of the fact that Microsoft's NETBIOS documentation is not very detailed, I have collected some relevant materials and added my own practical experience to write this series, I hope it will be helpful to everyone.
I originally wanted to write this series in the form of question and answer in order to increase readability, but I couldn't compile so many questions in my head at the moment. I still gave a brief introduction to Microsoft's browsing service step by step and then analyzed it in depth The specific working mechanism of NETBIOS, if you have any questions, you can ask us to discuss together.

The plan is divided into three parts, Microsoft Internet browsing process, in-depth analysis of NETBIOS, and network settings details

Introduction to the Microsoft Internet Browsing Process

In the book "Inside of Windows NT System Management Technology", a very representative problem was mentioned, and I excerpted it:

Question: Under what circumstances will the computer be visible but not accessible or accessible but not visible in Network Neighborhood? Please select the best answer: A. There is a physical problem with your network, such as a network cable B. The browsing service of Windows NTserver as the domain master browser is broken C. There is a problem with the Windows NTserver network card D. There is no problem with your network Is normal Microsoft browsing phenomenon

correct answer

The explanation in the book: Microsoft's web browsing may be "interrupted" in use, but in fact they are not interrupted. This misunderstanding is caused by the user's unfamiliarity with the process of Microsoft web browsing.

As students often complain, "Why are other people's online neighbors available, but mine is not?" "Why can sometimes be browsed, but sometimes unable to browse the Internet?" Xingling must also ring the bell, let us go See how Microsoft's web browsing is actually implemented. In view of the fact that you may not yet understand the concept of NT's "domain", most of the 98 machines have browsing failures. I will use 98 "workgroup mode" to explain to you.

1. What is a browsing list (Browsing List) In the Microsoft network, users can see all computers on the entire network (what? Subnet or broadcast domain? You can consider) in the browsing list. When you open the entire network through the Network Neighborhood window, you will see a list of workgroups, and then open a workgroup, you will see the list of computers inside (you can also use the net view / domain: workgroupname command in DOS mode Get), this is what we call Browsing List. Working groups are essentially a group of computers sharing a browse list. All work groups are equal. There is no rule that all computers cannot be in the same work group.

2. Where to browse the list I have seen a controversy on Kapok. Some people say: The computer list in the online neighborhood is obtained by broadcast query. But some people give a counter-example: My classmates are all shut down, but I can still see it in the online neighborhood, it should be obtained from the cache of relatively fixed devices such as HUB or switches. In fact, they are only right in one aspect. Combining the two of them is the correct answer --- Browsing the list is to query the browsing master server through broadcast, provided by the browsing master server.

3. What is the browsing master server? The browsing master server is one of the most important computers in the working group. It is responsible for maintaining the browsing list in this working group and specifying the master server list of other working groups. The other computers and other computers visiting this working group provide browsing services. Each working group selects a browsing master server for each transmission protocol, and the errors we often encounter that cannot browse the network are mostly because of where you are. The working group did not browse the main control server. You can use the NBTSTAT -a computername command in a workgroup to find the browsing master server that uses the NBT protocol. Its logo contains the \\ _ MSBROWSE_name field.

4. How is the browse master server specified? By default, the browse master server in the win98 workgroup is the first computer in the workgroup that enables file and printer sharing. It also allows manual configuration of a win98 computer To browse the main control server (the method will be described in detail later in the network configuration, but because the main control server needs to maintain a dynamic browsing list, performance will be affected), if multiple computers in a workgroup are configured with this option, or When the current browsing master server shuts down the system and no other computer enables the master control settings, the election of the master browser is required.

5. How to generate the election message about the browser by the browser control server through the browser election, it is not easy to capture the package, I have to tell it according to the things in the book. In fact, the process is very simple, first sent by a computer Election critical message, which contains information from the sending computer (operating system, version, and NETBIOS name, etc.), the election message is broadcast to the network, and each computer in the working group will use its own information and election message The priority comparison is mainly because the operating system plays a major role.Remember that it seems to be NT Server> NT WorkstaTIon> Win98> WFWG.Anyway, in the end, the one with the best conditions becomes the new browsing master server.

6. What is the process of browsing the entire network? When a win98 enters the network, if it has a server service (file and printer sharing is enabled), it will announce its existence to the network broadcast, and the browsing master server will get this announcement. And put it into the browse list maintained by itself; the computer that does not bind the file and printer sharing on the corresponding protocol will not be announced, so it will not appear in the network neighbor. When a client computer wants to obtain a list of required network resources, it will first broadcast a browse request. After the browse master server receives the request, if the request is a browse list of this group, it will directly send back the resource list required by the client; If the request is a browse list of other work groups, the browse master server will find the master browser of the corresponding work group according to the records in the Browsing List and return it to the user. The user can get the browse list it wants from there. As for how to share exchange resources with another computer, it is not the issue we are going to discuss here.

Understand the principle of web browsing, let me tell you a useful application. Now, for safety reasons, many students do not welcome strangers to visit their machines through online neighbors, but sometimes the lower movies need to be shared with known students. Come out, so file and printer sharing services cannot be deleted yet. How to do? Some people add a $ to the share name to achieve the hidden effect, but this can be seen using net share under DOS; some people add a password to the share, I heard that there are ways to crack it, and it is very It is easy to arouse the curiosity of "comrade hackers". Is there a way to hide my machine in a network neighborhood? For the classmates he knows, let him use \\ IP to visit. Right, the key is to prevent your machine from declaring yourself on the network, and I know that some of us have already made this a reality. As for the method, do n’t ask me.

Note: Because there is very little information about the win98 browsing service, and the books involved are mostly introduced in the "domain" model of NT, I can only test according to my own understanding in combination with the practice of netxray. The details are inevitable. Everyone correct me.

7. Why can't some machines be accessed in my Network Neighborhood? If Microsoft Network Neighborhood can really do what you see is what you get, I believe that people who complain about it will not be as many as they do now. You can use the previous introduction to browsing services. It is impossible to know that, because the browse list is not obtained by visiting each of them. Many times, the computers on the network cannot update the browse list correctly. When a computer shuts down normally, it will send a broadcast announcement to the network, so that the browsing master server will delete it from the browsing list in a timely manner; after abnormal shutdown, the browsing list will still keep the entry for a long time ( It is 45 minutes under NT), which is why we can still see it in Network Neighborhood. The stability of 98 is well known-it crashed before it was shut down ^-^

I wrote this first part here. I do n’t know how you feel. I think it ’s quite enjoyable, but I ca n’t solve any problems. For example, what are the necessary conditions for browsing the Internet, NetBEUI? TCP / IP? File and printer sharing or NETBIOS API? What is the principle of browsing remote host with \\ IP? Can I find computers across routers? Students who like hands-on can use Netxray to figure it out for themselves. If you are lazy, be prepared to wait for the next part-in-depth analysis of NETBIOS.

In-depth analysis of NETBIOS

In this part, I will first give a basic introduction to NETBIOS, and then mainly explain the characteristics of NETBIOS in terms of LANA number, NETBIOS name table, and NBT, so that everyone can understand the principle of NETBIOS interface communication. And master the method of using NETBIOS name table to identify network neighbor browsing faults and how to eliminate them. Which may need to use some network commands, such as net, nbtstat, etc. If there are students who will not use it, please refer to the windows help documentation (it is best to look at NT, 98 is a little scum), and I will not explain it here.

Students familiar with network programming know that there are two important network APIs under Windows, WINSOCK and NETBIOS. We usually use IE to browse the web, use FOXMAIL to send and receive emails, and use OICQ to chat all use WINSOCK API. However, some network applications need to use the traditional network interface NETBIOS. Browsing online neighbors and sharing files are typical of them. Although Microsoft has added access to the AF_NETBIOS address family in its latest WINSOCK API, and intends to make support of the NETBIOS API optional from its win2000, the real demise of NETBIOS will still take time. Here I don't want to open up the history of NETBIOS to judge its pros and cons and waste everyone's time. Existence is the truth, and we get to the point. The biggest advantage of the NETBIOS API is that it makes the programming interface "independent of the protocol" --- the application can run through TCP / IP, NetBEUI and IPX / SPX.

举个例子来说，如果你在网络属性里同时添加了这三种协议，那当你通过网上邻居浏览某台机子的资源时能确定用的是哪种协议在和它进行通信吗？不过由于这种“与协议无关”性是通过对传输协议本身进行改造，在相应协议上添加NETBIOS接口实现的，所以也就产生了一些局限性：

一是并非所有的协议都支持NETBIOS，我们知道的就只有上面提到的那三种协议实施了NETBIOS接口（也许在它们前面加个Microsoft标识更恰当些）；

二就是我在前面提过的LANA编号的问题了，LANA号的提法在多宿主机环境下可能更准确些，对于我们一般只安装有一块网卡的机子来说大家就把它简单理解成一种通讯协议的对称性就可以了。

举个例子，A只安装了TCP/IP，B只安装了NetBEUI，虽然他们都在协议上绑定了NETBIOS接口，但彼此在网络邻居里是看不到的。这也提醒我们要想在网络邻居里看到最多的机子，就要把三个协议全部安装。为了后文叙述的方便，我们把启用了NETBIOS的三种协议分别用一个名字来表示：NetBT/NBT（TCP/IP）、Nbf（NetBEUI）、NwlnkNb（IPX/SPX），它们各对应一个LANA号，只有相同的LANA号之间才能建立通信连接。

接下来要说的就是最为关键的NETBIOS名字的问题了。对于BSD系统，每台机器都有一个主机名，从而也引出了DNS的概念，这也可以说是UNIX和TCP/IP紧密结合的产物。而Windows可没有跟某种协议有近亲关系，在它眼里只有机器名（即NETBIOS名）才是最关键的。

在win32环境中，针对每个可用的LANA编号，每个进程都会为其维持一张NETBIOS名字表。我们可以用nbtstat -n命令获得本机与NBT相关的名字表（你要是连TCP/IP都没安，可别来问我为什么不能用）。NETBIOS 名字分两种类型：唯一名（UNIQUE）和组名（GROUP）。唯一名很好理解，就是说在同一子网上要独一为二（注意我这里没有用广播域，这在我的第三部分里我会结合以前的一些讨论详作说明）；而组名的作用是可以实现多播数据通讯。结构上也由两部分组成：字符串和Scope ID。这里的字符串就是我们给自己的计算机、工作组起的名字，而且对所能使用的字符及其长度都有限制，大家自己去查书，我就不在这里浪费时间了，需要说明的是一些同学为了“隐藏”自己，把自己的机器名起的象个IP一样，如0.0.0.0(真不知是那位高人教大家的，呵呵）其实字符“."是不允许做机器名的，从这个角度讲win98真是太渣渣了（误导群众，怪不得老死机，该！）而NT在这方面做的就好多了。我主要讲解的是Scope ID域，它占用NETBIOS名的最后一个字节，最大的作用莫过于可以标识不同的Microsoft 网络服务了，因为它是NETBIOS名的一部分，因此UNIQUE name允许两台computername 相同，但scope ID不同的计算机在同一子网上存在。我不打算摘抄大段的NETBIOS 标识符给大家，这里就以我机子上的一个NETBIOS名字表为例给大家讲解一下常用的NETBIOS标识符类型：

C:\>nbtstat -n NetBIOS Remote Machine Name Table Name Type Status ---------------------------------------------
CJT <00> UNIQUE Registered
CJT<00>代表工作站服务，每一台上网的计算机必须首先注册的唯一标识符，这也是进行网络邻居浏览的唯一必要条件。在同一子网上的其它机子可以用ping CJT得到我的IP，注意这可跟DNS没有关系，是通过广播查询CJT<00>得到的，因为TCP/IP和NETBIOS有绑定。

MINEGROUP <00> GROUP Registered

这条没什么可说的，但凡把工作组名设成MINEGROUP的机子都会注册这一项，从而同一子网上的某些机子间建立一种特定的逻辑关联，使对于MINEGROUP<00>进行的通讯只被这些机子接收，这里大家可以考虑不在MINEGROUP的机子对这些报文的处理过程。虽说这一项是名字表里最不重要的一项，但大多数同学无法浏览网上邻居的故障却都和它有关哦！等会儿我会说明。还有大家可以想想，要是你的工作组名和别人的机器名起的一样会出现什么事情呢？

CJT <03> UNIQUE Registered CJT<03>代表消息服务，就是那个在win2000下突然弹出个窗口来说“某某某侵犯版权” 的东东。其实这是个挺好的服务，可以让我们用win9X下的WINPOPUP和winNT下的NET SEND 进行简单的消息传送。不过在NT下,CJT<03>只代表消息的接收端，要发送消息，还需注册一个CJT<01>，这也是NT第一次用net send发消息要等很久的原因，因为CJT<01>只在你用到net send时才会去注册；而9X下只用一个CJT<03>就把收发全搞定了。不过那个WINPOPUP好象不能给自己发消息耶，真不知微软在搞啥子。

CJT <20> UNIQUE Registered 与CJT<00>相对照，CJT<20>代表服务器服务，我前面已经说过，凡是提供文件及打印机共享服务的机子就叫做SERVER，它会在入网时进行浏览器宣告，这也是一台机子可通过网上邻居“被”访问的唯一必要条件。

MINEGROUP <1E> GROUP Registered 还记得我前面说过的那个浏览器选举吗？我把<1E>标志称为候选者，这样当MINEGROUP组里的当前浏览主控服务器当机后，所有拥有<1E>标志的机子都有资格参加竞选。至于这个标志是怎么来的，记住一句话：SERVER完全同意作为默认的候选浏览主控服务器。关于这句话的理解，我后面将有一道题帮助大家认识它。

XIXI <03> UNIQUE Registered 咦？又一个<03>,这个XIXI是啥子东西？其实XIXI就是CJT的用户名了，就是那个登录提示框里的东西。使我们除了通过对方的机器名以外还可以通过他的用户名给对方发消息。不过要是和别人的名字发生了重复怎么办？会报冲突吗？ will not.因为这个XIXI<03>是我们在按了回车车键以后才进行注册的。写到这里，不禁对以前那个ESC键的问题有所领悟，

原来所谓的登录网络就是干了这么一件事，那如果...如果...，企不是...呵呵，搞个测

试先。

MINEGROUP <1D> UNIQUE Registered 这个<1D>想来大家都已经猜到了，就是表明CJT是MINEGROUP里的浏览主控服务器了，当“领导”的感觉总是这么爽。嘻嘻

..__MSBROWSE__.<01> GROUP Registered 见过这个怪东西的人肯定不少，但真正知道它用途的恐怕不多。这是一个组名，由整个子网上的所有浏览主控服务器构成，这样当MINEGROUP里的机子想要浏览其他组的资源时，CJT就凭借这个标识为大家查找那个组的浏览主控服务器，从而使我们能获得该组的浏览列表。 基本的一些标识符类型就介绍完了，只要掌握了这些，解决常见的浏览器故障已是绰

绰有余了，通过后面的一道习题大家可以实践掌握这种方法。对于还想进一步了解更多标识符类型的同学可以使用net start命令获知其它的微软服务，大多数服务都有一种标识符与其相对应。

MAC Address = 00-88-CC-23-15-54 前面POPO曾说过，使用nbtstat -A IP可以获知远程主机的MAC，至于原理，就是我们在这里最后要说的NBT了。现在大家已经知道，NBT就是建立在TCP/IP传送协议之上的NETBIOS接口，我们先将它与Nbf进行一番对比。Nbf指的是NETBIOS帧协议，以NetBEUI为基础，这可是真正的架构在链路层之上的协议哦，不过也因为它是在LLC上面，所以无法路由。只有借助一些可路由协议（如IP或IPX）才能实现跨广播域浏览因为TCP/IP发展最为迅速，最为普及，NBT也才受到大家如此的关注。

NBT提供的服务可以分成三类：名称服务（UDP137）、数据报服务（UDP138）和会话服务（TCP139）。 1）名称服务主要用于广播解决本子网的NETBIOS名和IP地址转换的关系，比如我前面那个ping CJT的例子。因为NBT是建立在TCP/IP之上，而建立TCP/IP通讯是必须知晓双方IP 地址的，这跟Nbf直接用MAC地址通讯很不一样。但也因为使用的是UDP广播，所以名称服务无法跨越路由器。（这里我们只针对b-节点，不对WINS加以介绍） 2）数据报服务提供了无连接和面向广播的通信方式。它主要用于浏览列表通知，我前面也说过我们桌面上的那个网上邻居就是它构建的，此外我们用NET SEND *命令给计算机组发消息时也是靠它的UDP广播（多播）能力。但也正因为它使用了UDP传输层协议，因而在跨越路由器时也会遇到与名称服务相同的问题。 3）使用面向连接TCP协议的会话服务才是我们的救星，因为它可以跨越路由器。网络中产生的NETBIOS通信主要也是因为会话服务的使用，而文件和打印机共享服务则构成了会话服务通信的主体。

说到这里就不得不提SMB（Server Message Block），不过要讲清楚SMB，可能要从NCB的由来说起，那可就又是一个长篇了。这里我就教给那些还不太明白它们之间关系的同学一个简单的办法，虽不太准确，但挺实用，希望清楚的同学别给我戴上误导群众的高帽哦：-）首先SMB是一种协议，一种“应用层”的协议，一种基于SERVER/CLIENT架构的应用层协议，大家完全可以把它看成是一种HTTP，FTP或是TEL NET 而添加了文件及打印机共享服务的机子就是SERVER端，可以被其它工作站和服务器访问如果没有添加文件及打印机共享服务，则不能被其他机子访问。当然，SMB除了提供文件及打印机服务以外，还可以进行会话控制和交换消息，如用net send命令可直接把使用消息类型的SMB包发给特定计算机。而且因为会话服务是建立在TCP上的，只要你能获知远程主机IP，就可以跨越路由器。

总算不负大家所托，又凑了一篇，就不知大家看了以后是不是失望大于期望呢：-）原理的学习毕竟是枯燥的，但也是必须的。因为篇幅和水平有限，很多地方的介绍我都简略了，可能有些同学读起来会稍感困难，在后面我转了一些概念性的文档以帮助大家阅读。其实说句实话，与其看这些东西倒不如找个netxray来，亲自抓包看看到底在你打开网上邻居，开关机，共享文件，进行名字解析，名字注册时自己的机器干了些什么，远比我这东一句西一句的乱讲要强多了。 至于那些“死逮着我不放”的同学，要看下一篇，只好再等等了。

我新购的网卡在电脑上无法安装，而在其他电脑上却使用正常，这是怎么回事？

答：如果在电脑中安装好网卡后，系统没有提示找到新硬件，你可运行“添加新硬件向导”来让系统搜索新硬件。方法是单击“开始”，指向“设置”，单击“控制面板”，然后再双击“添加新硬件”。按照屏幕提示操作。你可选“让Windows搜索新硬件吗？”，单击“是（推荐）”，然后再单击“下一步”，让系统找到网卡再安装其驱动。

而如果出现以下任何现象，网卡或者网卡所在的插槽损坏：

1、“添加新硬件向导”检测不到网卡；

2、“添加新硬件向导”能够检测到网卡，但无法正常工作。

为了确定到底是网卡还是插槽的问题，可以检查网卡是否牢靠插入插槽之中。如果网卡已牢靠插入插槽之中，请改插到其他插槽之中试试。如果问题仍未解决，则可能是网卡损坏或与你的电脑不兼容，可更换之。

问：我访问局域网中的计算机时，为什么常常被提示要输入用户名和密码？

答：这主要是为了安全方面的考虑。而且当你重新启动计算机时又要重新输入用户名和密码，这一点确实让人会觉得很麻烦。

你只要在需要进行文件共享的计算机上建立一个相同的用户名，并且使用相同的密码，然后局域网中的计算机都利用这个用户名和密码登录，这样在网上邻居中访问对方计算机时就不需要输入用户名和密码了。

笑解局域网故障

1、四台机器通过一八口HUB连到CISCO1900交换机，连网速度严重变慢，查网线正常，判断四块网卡同时故障可能性不存在， HUB经验证也正常，后检查交换机发现连接该HUB的端口被设为双工，改为单工后网络恢复正常。这里应注意：连到HUB的端口不能设为双工！

2、一台机器，杂牌8139网卡，以60米网线连于集线器，使用中突然不能上网，集线器指示灯亦熄灭，用网线测试仪测试网线正常，检查系统，网卡也正常工作，重做水晶头后故障依旧，怀疑网卡驱动能力下降，准备更换网卡。抱着试试看的想法关掉接线板电源，重新开机后却发现网络已连通。可见故障是网卡工作不稳定造成。

3、一台机器，D-LINK530TX网卡，连于100M交换机，WINXP操作系统，加入WIN2000域，登录速度非常慢，登录后网络访问速度让人无法容忍，测试网线100M通联正常，怀疑为软件原因，于是重装网卡驱动，无效，试替换网卡，网络访问速度立即恢复正常。我们在分析局域网故障原因时，不能想当然认为只要能上网，网卡就没问题，本例这一故障现象笔者已碰到多次，确为网卡原因。

如何利用空闲的网络端口

问:学校的教室里有很多空闲的网络端口，虽然我带着笔记本电脑，但是不知道它们是否能够连接到交换机，并且不清楚IP地址（我们使用的是静态IP）、子网掩码、默认网关、DNS等信息。该用什么方法连通网络呢？

答：可以通过以下方式测试端口，以便连通网络。

1.将笔记本电脑接入空闲端口，如果笔记本电脑网卡的指示灯开始闪烁，说明已经连接到局域网。如果网卡的信号指示灯不亮，说明该端口没有从配线架连接交换机，无法接入网络。

2.如果网络规模较小，可能没有划分VLAN。这样，网络内任何计算机的IP地址信息完全相同，查看一下其他计算机的IP地址信息，再为自己的计算机进行设置。需要注意的是，子网掩码、默认网关、DNS应当与其他计算机相同，而IP地址应当与其他计算机不同。另外，一些不太“吉利”的IP地址可能被空出不用，所以，不妨选出来试试。

3.如果网络规模较大，可能会划分VLAN。 VLAN的划分是有规律的，通常是按照部门来划分的。因此，可以根据端口的位置判断其所在的VLAN。同一VLAN内的子网掩码、默认网关、DNS信息是相同的。可以查看一下相邻计算机的IP地址信息，然后尝试设置。

4.如果网络采用动态IP地址分配，则只须将计算机设置为“自动获取IP地址”即可。

提醒大家：IP地址由网络中心统一管理，私自设置IP地址很有可能会导致IP地址冲突，造成网络通讯和网络服务的中断。

网段不同，能互访服务器吗

问：一台服务器安装了Windows 2000系统并设置为Web服务器和FTP服务器，同一网段的计算机就可以访问这台服务器。是否有方法可以让不同网段的计算机也可以访问Web服务器和FTP服务器呢？

答：可以根据不同情况分别处理：

1.如果所有的计算机都位于同一网络，仅仅是划分了不同的IP地址，那么，仅为该服务器指定不同网段的IP地址即可。

2.如果不同网段的计算机位于不同的网络（VLAN），那么，只要不同网络之间能够相互通讯，就可以实现对Web服务器和FTP服务器的访问。不同网络之间可以借助于网桥和三层设备（三层交换机或路由器）实现通讯。

3.如果不同网段之间不能进行通讯，可以在服务器上再安装几块网卡，分别连接至不同的网络，分别指定相应网络的IP地址信息，但默认网关只能设置一个。

Failure phenomenon:

一日在上网的过程中我接连打开了几个网页，由于网页上有图片，下载的速度比较慢，我于是又同时打开了Foxmail邮件客户端来接收邮件，这时我发现网络忽然停滞了下来，不但经常连接的邮件服务器连不通，而且所有的网页下载都同时停止了响应，我的上网主机陷入了瘫痪状态。

Processing process:
一、我的第一反应是主机的病毒发作或是中了网页木马。于是立即关闭了所有的应用程序，关闭了Windows2000操作系统，用干净的引导软盘启动系统后，迅速加载防病毒防木马程序对系统进行一次全面的清剿。这一过程足足耗时40多分钟，结果却一无所获。

二、而后我怀疑是局域网出了问题。重启系统以后，依次点击系统菜单中的“开始——运行”，在弹出的对话框中输入CMD并回车，进入DOS命令行窗口，敲入“ping 网关IP 地址”，系统响应“Request TIme Out”，看来问题是由网络本身所引起的。通过询问公司同事获知，他们的上网一切正常。于是可以确定问题不在局域网，而是出在本机自身的网络部分。

三、首先考虑到的当然是相对脆弱的网线了。但是当我用“替换法”将本机的网线拔下，插入到局域网中另外一台同样配置的主机上时，其网络的速度却运作如飞，于是就可以排除网线自身质量原因所造成的问题。

四、最后的目光只能聚集在这台主机的内置网卡上了。这个集成在主板上的网卡，最近因为网络的调整而经常进行网线的拔插，是否是因为接口部分接触不良或是网卡的固定部分发生了松动所造成的呢？我于是再次关闭了主机，打开机箱的面板，找到内置网卡的所在，用手将其重新固定校正。而后再次启动系统，打开浏览器，呵！上网速度恢复如初。为了确保网络故障不再重演，我又重复了一下引发网络故障的上述操作，网络仍然能够保持畅通。这就证明了问题的罪魁祸首是出在主板的内置网卡上了
网络经常会出现故障，就如人会经常生病一样，在出现网络问题之后，最重要的是不要着急，头脑要保持清醒。查清问题出在哪里，一般有以下几种情况：

一、当整个网络都不通时，可能是交换机或集线器的问题，要看交换机或集线器是否在正常工作。

二、只有一台电脑网络不通，即打开这台电脑的“网络邻居”时只能看到本地计算机，而看不到其它计算机，可能是网卡和交换机的连接有问题，那么我们首先要看一下RJ-45水晶头是不是接触不良。然后再用测线仪，测试一下线路是否断裂。最后要检查一下交换机上的端口是否正常工作。

三、在“网络邻居”中不能看到本地计算机，或打开“开始/运行”中用“PING”命令，“PING”本地计算机的IP地址不通时，说明你的网络设置有问题，那么首先想到的应该是网卡，我们可以打开“控制面板/系统/设备管理/网络适配器”设置窗口，在该窗口中检查一下有无中断号及I/O地址冲突，一般情况下NE2000系列的网卡为IRQ3，8029芯片的网卡为IRQ10。如发现网卡没有冲突，下一步就要检查驱动程序是否完好，然后重新安装网卡的驱动程序。

四、在“网络邻居”中能看到网络中其它的计算机，但你不能对它们进行访问，那么可能是你的网络协议设置有问题。把你以前的网络协议删除后，再重新安装，并重新设置。

问题1:逮捕物理层的滥用者
-用户抱怨-不能登陆或时断时续
-症状-只影响一个工作站，而该站原先没有问题
-查找问题：
电缆终端链路太长。用户每天都移动，弯曲，连接和切断网络终端（尤其时膝上型笔记本电脑）。廉价的电缆测试仪就能检查这种问题。在你能确切地说是电缆的问题之前，通常首先考虑不是电缆的问题。这需要使用网络测试工具来证明本地网段的健康状况是否良好，集线器端口功能是否正常，网卡及其驱动程序工作是否良好。最后，检查网络互连设备是否有问题。只有此时，你才会知道为了孤立有问题的终端，断开的连接器或是接地回路等问题该从何处着手测试电缆。在铜轴线网络中，搜寻在同轴“T型头”和网卡之间的断头，在UTP网络中，连续运行仪器图测试功能，不断扭动终端以识别接触不良或短路。
-解决问题：
更换工作站连接电缆，更换损坏的连接器，或者必要的话停止使用水平电缆。再次全面检查处理过的电缆。

问题2：快速以太网比升级前的以太网还慢
-用户抱怨-10Mbps的以太网速度慢，升级为100Mbps快速以太网后甚至不能连接上网。
-症状-影响新工作站或升级的工作站连接上网。
-查找问题：
对于UTP5类非屏蔽双绞线，用电缆测试仪测试其是否符合对应100Mbps传输速率的EIA/TIA-TSB67标准。某些在10Mbps以太网工作正常的电缆链路因为近端串扰太大在100Mbps以太网就不能正常工作。信号耦合到邻近线对引起高频信号传输失败。将UTP的线对分开甚至会使网络在达到一定流量时瘫痪。
-解决问题：
更换或停用不能连接的链路，故障清除后再全部测试处置过的链路。
问题3:无效的看门狗
-用户抱怨-不能连接Novell网络的Netware远程服务器
-症状-影响本网段内与服务器相连的所有工作站－查找问题：
检查网段的健康状况，注意观察其利用率，碰撞，错误帧和广播帧水平。此时可观察到大量的碰撞或错误帧，该碰撞或错误帧可引起客户机和服务器之间“Hello”帧出现延迟。再某仪指定的服务器所再的远端网段重复此测试。如果两个网段都出现空白，用网络测试仪向路由器中的SNMP代理查询，检查两个网段之间的路由表。确定该路径不存在拥挤问题。为了有效地使用资源，在看门狗允许地时间内如果客户机对“Hello”帧无反应，则Novell服务器会将该客户机注销。
-解决问题：
简便地方法时改变看门狗时延地参数，将Novell服务器中的该参数改大。如果情况有所改善，则可确定为引起帧丢失的原因，纠正看门狗延时帧计时器的参数。

问题4:刍菊链效应
-用户抱怨-网络服务变慢
-症状-影响某个以太网段的所有用户。网络服务（访问服务器）变慢，但与所连接的某的服务器无关。
-查找问题：
在高峰时段将网络测试仪连入集线器，运行网络健康状况测试。此时将会观察到大量错误帧。在10BASE-2网络中，错误帧的类型归类为“延迟碰撞”。在10BASE-T网络中帧错误的类型归类为典型的帧校念序列错误（FCS错误），随着网络用户的增长，新增加的集线器通常与原来的集线器形成效应。
-解决问题：
统计一下任意两个网络设备之间经过的中继器的数量。在10Mbps以太网中不应超过4个，在100Nbps快速以太网中不应超过2个。如果数量超标，则按以太网的标准修正网络拓扑结构，然后再错误帧是否还出现。
问题5:IP网络管理者的报应
-用户抱怨-一个工作站间隙性出错，不能登陆或者不能访问远端服务器
-症状-只影响一个工作站，通常在增加、移动、变更工作站后出现此问题
-查找问题：
先排除用户是否有帐户和安全设置方面的潜在问题。让用户登陆并且试图从另一个工作站重复这一操作。如果成功，则可以用网络测试仪从用户端到服务器之间的链路状况。然后测试网卡

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