Common fault problems in wireless LAN

If there is a problem with your wireless network, the reason may be from all aspects. When you try to solve this problem, it may involve many factors such as hardware manufacturer and network configuration.

When a problem occurs in a wireless network, you should start with several key issues. Some hardware problems can cause network errors, and bad configuration can cause the network to not function properly. In this article, we will describe some of the ways and tricks of wireless network scheduling. (This article is for basic wireless networks, not special wireless networks)

　　Hardware row Error

When there is only one access point and a wireless client connection problem, we may quickly find the client with the problem. But when the Internet is very large, it may not be easy to find out where the problem is.

In a large wireless network environment, if some users are unable to connect to the network, while others do not have any problems, it is likely that one of the many access points is faulted. In general, by looking at the physical location of a client with a network problem, you can probably determine which access point is having a problem.

When all customers are unable to connect to the network, the problem may come from many ways. If your network uses only one access point, the access point may have a hardware problem or an incorrect configuration. In addition, it may be due to radio interference is too strong, or the wireless access point and the connection between the wired network problems.

　　Check the accessibility of an access point

To determine why you cannot connect to a network problem, first check to see if the computer in your network environment can connect to the wireless access point properly. The simple detection method is to open the command line mode on one computer in your wired network, and then ping the IP address of the wireless access point, if the wireless access point responds to the ping command, then the computer in the wired network can be verified to be connected to the wireless access point properly. If the wireless access point is not responding, there may be a problem with the wireless connection between the computer and the wireless access point, or the wireless access point itself has failed. To determine what the problem is, you can try to ping the wireless access point IP address from the wireless client, if successful, that the computer's network connection part of the problem may have occurred, such as cable damage.

If the wireless client is unable to ping to the wireless access point, then the wireless access point itself is working abnormally. You can restart it, wait about five minutes, and then use the ping command to see its connectivity through the computers and wireless clients in the wired network.

If the wireless access point is still not responding in both respects, it is proven that the wireless access point is corrupted or misconfigured. At this point, you can connect the potentially corrupted wireless access point to a functioning network via a usable cable, and you will also need to check its TCP/IP configuration. After that, ping the wireless access point again on the wired network client, and if it still fails, the wireless access point is corrupted. Then you should replace the new wireless access point.

　　Configuration issues

The quality of the wireless network device itself can generally be trusted, so the biggest source of problem is the configuration of the device, not the hardware itself. With this in mind, let's look at several common network connectivity failures due to bad configuration.

　　Test signal strength

If you can ping a wireless access point directly through a network cable, and you cannot ping it wirelessly, you can basically assume that the fault of the wireless access point is only temporary. If the problem has not been resolved after debugging, then you can check the signal strength of the access point. Although for most network management, there is no standard measure of wireless signal strength, but most wireless network card manufacturers will include a measure of signal strength in the network card mechanism.

　　Try changing the channel.

If you have been tested and you find that the signal strength is weak, but have not made any changes recently, you can try to change the channel of the wireless access point and test the signal through a wireless terminal. Since modifying the connection channel on all wireless terminals is not a small project, you should first test on a wireless terminal to prove that it is effective before it can be implemented in large areas. Remember, sometimes the failure of a wireless network can be suddenly improved by the fact that an employee hangs up the phone or shuts down the microwave.

Not long ago, I took my notebook to a friend's house to work. I decided to connect to his network because my friend's family also adopted a wireless network. When I got home, I didn't use the notebook any more. After two weeks, when I opened my notebook again, I found it was unable to connect to my wireless network. Soon I found the root of the problem: I forgot to change the service area identifier (Ssid,service Set Identifier) back to my own network ID. Remember, if your SSID does not properly specify the network, then your notebook will not ping the wireless access point, it will ignore the wireless access point, the given SSID to search for the corresponding access point.

　　Verify WEP Key

Check the WEP encryption settings. If WEP is set incorrectly, you will also not be able to ping wireless access points from the wireless terminal. Wireless adapters and access points for different vendors require you to specify a different WEP key. For example, some wireless cards require you to enter a hexadecimal-formatted key, while others require you to enter a decimal key. Similarly, some vendors use 40-bit and 64-bit encryption, while others only support 128-bit encryption.

For WEP to work properly, all wireless clients and access points must match correctly. Many times, although the wireless client appears to have configured WEP correctly, it is still unable to communicate with the wireless access point. In this case, I typically return the wireless access point to the factory state, re-enter the WEP configuration information, and start the WEP feature.

　　Tricky WEP configuration issues

Until now, the most common configuration-related issue is the use of the WEP protocol. The problem with WEP is also tricky because the symptoms of WEP mismatch are very similar to many serious problems. For example, if the WEP configuration is incorrect, the wireless client will not be able to obtain an IP address from the DHCP server on the wireless network (even if the wireless access point has no DHCP capabilities). If the wireless client uses a static IP address, it will not be able to ping the IP address of the wireless access point, which is often mistaken for the network is not connected.

The basic technique for determining whether a WEP configuration error or a network hardware failure is the use of wireless network card drivers and the built-in diagnostic capabilities of the operating system. For example, one of my notebooks uses a Windows XP system and is equipped with a Linksys wireless network card. When I move the mouse over the wireless network icon in the system tray, a summary of the network connection information as shown in figure a emerges. As you can see from the diagram, the network connection is quite normal. When the connection channel and SSID are set correctly, you can connect to the wireless access point even if WEP is set incorrectly. At this point, you will see from the taskbar that the connection signal has a strength of zero. The Linksys NIC displays the connection signal strength regardless of whether WEP is set correctly. You can also see that the network is actually connected, although it may not be able to ping to the wireless access point.

If you right-click the wireless network icon in the taskbar and select View Available Wireless Networks from the pop-up menu, you will see the wireless network connection (Wireless network Connection) Dialogue window. This dialog window displays the SSID number of all the wireless networks in the current channel, including the network on which you are not connected. So if you find your wireless network number in the list, but you don't seem to be able to connect properly, then you can be assured that there is no problem with your network connection, the problem is in the configuration.

Note: The Wireless Network Connection dialog box also provides an area where you can enter a WEP key, and you can enter the WEP key for that network when you try to connect to a wireless network. There were times when I was unable to connect to the destination network correctly, and was successful by entering the WEP key manually in this area. Typically, after you enter the WEP key here, the network will immediately connect successfully.

　　DHCP Configuration Issues

Another reason that you cannot successfully access a wireless network may be caused by a DHCP configuration error. A DHCP server in a network can be said to be a key factor in your ability to use your wireless network properly.

Many new wireless access points have their own DHCP server capabilities. In general, these DHCP servers assign 192.168.0.x this address segment to the wireless client. Also, the DHCP access point does not accept connection requests that are not IP addresses assigned by themselves. This means that a wireless client with a static IP address, or a client that obtains an IP address from another DHCP server, may not be able to connect to this access point properly.

When I first installed a wireless access point with a DHCP service, I allowed it to assign an IP address to my wireless terminal. However, the IP address segment of My network is 147.100.x.y, which means that although a wireless client can connect to a wireless access point and get an IP address, the notebook will not be able to communicate with other computers in the wired network because they belong to different address segments.

　　There are two ways to do this:

Disables the DHCP service for the access point and allows the wireless client to obtain an IP address from a standard DHCP server within the network.

Modify the address range of the DHCP service so that it applies to your existing network.

Both of these methods are feasible, but it depends on the firmware features of your wireless access point. Many wireless access points allow you to use one of these methods, and there are few wireless access points that can support both approaches.

　　Problems with multiple access points

Imagine if there are two wireless access points that work in the default way. In this case, each access point assigns a 192.168.0.X IP address to the wireless client. The resulting problem is that two wireless access points do not distinguish which IP is allocated by itself, and which is allocated by another access point. Therefore, the problem of IP address conflict will be generated in the network sooner or later. To solve this problem, you should set a different IP address allocation range at each access point to prevent address duplication.

　　Note Customer List

Some access points come with a list of customers, and only the end customers in the list can access the access point, so this may also be a source of network problems. This list records the MAC addresses of all wireless terminals that can access the access point, and from a security standpoint, it prevents unauthorized users from connecting to your network. Normally this feature is not activated, but if the user accidentally activates the customer list, then because no MAC address is saved in the list, none of the wireless clients can connect to the access point, regardless of the other settings.

I've also met the problem caused by setting up a user list when there are multiple access points in the network. Some administrators think that they can access any access point on the network as long as they have a client list set up at an access point. In fact, if you want the access point to activate the Client List feature to improve security, you should make the same settings on each access point in the network so that the authenticated user can connect to any one of the network's access points, while an unauthenticated user cannot connect to any one.