Although wireless LANs are easy to install and setup, troubleshooting them can be a nightmare.

You will likely encounter troubles with an 802.11 deployment because of unplanned environmental changes, for example office relocation or change in the physical setting, utilization growth, security breaches, and improper configuration parameters.

Typical wireless LAN hardware consists of PC Card wireless LAN adapters and wireless LAN access points (APs). The APs are quite resilient when it comes to hardware problems as they reside at one location and are normally not handled by users.

However, PC Cards are vulnerable to a number of hardware and software problems because they are removable devices and users of computer notebooks and laptops often remove them to use other PC Card devices.

In this section, we examine the most common hardware−and software−related problems that wireless LAN adapters and APs suffer from.

Hardware Problems

Hardware problems can be easily recognized through better understanding of the wireless LAN equipment. This includes becoming familiar with the model and features of the products, the functions of light indicators on the AP and wireless LAN adapters, specific technologies involved, and their installation procedures.

The paragraphs that follow describe some of the common hardware−related problems.

• Disconnected AP Power or Network Cable

Access points normally suffer from this problem where the electric power to the APs gets disconnected due to a human mistake. This problem is easy to detect, as APs without power will not send any periodic beacon, which they normally would send out.

• Inoperable Technology Use

If an 802.11b wireless LAN card is used in an 802.11a wireless LAN, it will not work. The problem can be diagnosed by carefully examining the physical wireless LAN adapter to ensure that it is compatible with the AP in the LAN.

• Antenna Diversity

If the antenna of an AP gets broken, the AP might not work at all or may provide extremely poor performance. APs should be monitored periodically to ensure that the antennas are properly installed.

• Older Firmware

Often wireless LAN manufacturers publish newer firmware, which can be uploaded into the wireless LAN adapter or the AP.

Sometimes only one of the components, either the wireless LAN adapter or the AP, is upgraded with new firmware and the other device is not, making both incompatible and inoperable with each other.

Any time a firmware upgrade is performed, all other devices should be made checked to ensure compatibility with the new firmware.

• Equipment Failure

In case of an equipment failure, you may need to quickly provision and configure new hardware components. To ensure that this can be done in a timely manner, you must record all configuration and customization information, for example AP passwords and WEP keys, about your APs and other wireless LAN equipment.

• Mishandling of Wireless LAN Adapters

Most mobile computers use PC Card−based wireless LAN adapters. PC Cards are sensitive hardware devices. Often they get dropped on the floor by mistake, resulting in internal circuit breakdown.

Often signs for such breakdown occur when a computer might not recognize the card at all or gets hung when booted. If such a problem is noticed, try using a different wireless LAN card on the computer where the problem is noticed.

If the other card does not demonstrate this problem, it's likely that the first card has gone bad.

• Cable Problems

Wireless APs are radio devices, and all cables connecting to them must be of high quality. Use high−quality shielded cables to ensure that there are no unintended radio frequency leakages to interfere with the AP radio signals.

The antenna cables should not be longer than specified by the wireless LAN device manufacturer. The longer the antenna cable, the lower the signal strength; consequently, the lower the range.

To ensure cable−related interference problems, you should avoid the following:

• The connections to either end of the antenna cable must be secured. Loose cables result in degraded radio quality.
• Avoid using cables that show physical signs of damage. Antenna cables with obvious physical damage can result in degraded radio signals.
• Avoid shared antennas and power cable runs. Power cables can produce electromagnetic interference that may affect the signal in the antenna cables within close proximity.

Effect of Building Material on Wireless LANs

The building material at a wireless LAN site affects the performance of the LAN. The following table illustrates the maximum number of walls that can be present between access points and wireless LAN adapters without any degradation of the coverage.

• Paper or vinyl walls - Maximal Wall Between AP and Antena = No impact on signal
• Solid or precast concrete walls - Maximal Wall Between AP and Antena = 1 or 2
• Concrete block - Maximal Wall Between AP and Antena = 3 or 4
• Wood or dry wall - Maximal Wall Between AP and Antena = 5 or 6
• Metal walls - Maximal Wall Between AP and Antena = 0

Software Problems

Because APs are always fewer in a wireless LAN compared to the number of wireless LAN adapters in a wireless LAN, the software problems are more common among wireless LANs.

Some of these problems may be discovered when the wireless LAN adapter is set up, while others may arise any time during the use of a wireless LAN. Some of the common software−related problems are described in the list that follow.

• Incorrect Configuration

Wireless LAN adapters do not have many configuration problems, so it is easy to overlook them when configuring a wireless LAN adapter.

The common configuration problems include incorrect selection of wireless LAN operation mode and channel settings. For example, if the LAN is operating in infrastructure mode and the adapter is configured for the ad−hoc mode, the LAN adapter will not be able to participate in the wireless LAN.

• WEP Encryption Setting

If a wireless LAN AP is configured to use WEP encryption and the wireless LAN adapters are not, the network will not function because the wireless LAN AP will be communicating in the encrypted mode, whereas wireless LAN adapters will be communicating in unencrypted mode.

To make sure that such a problem does not arise, you should make sure that anyone responsible for or capable of modifying the adapter settings is aware of the encryption mode used in the wireless LAN.

• Incorrect Extended Service Set Identifier (ESSID)

In infrastructure mode, each AP is assigned an ESSID. All wireless LAN adapters that need to communicate with an AP, or group of APs, must be configured with the correct ESSID.

You need to further ensure that if multiple wireless LANs are within the radio range and you want to isolate them, you must use a unique ESSID.

• Software Installation Problems

If an incorrect version of software or the wrong software driver for wireless LAN adapter is installed on a computer, the adapter will not function at all and the computer will not be able to participate in the wireless LAN.

To ensure that you are installing the correct software drivers, consult the wireless LAN adapter manuals or contact the manufacturer.

• Authentication Problems

If you are using the 802.1X authentication protocol, you should make sure that you are using the correct credentials to prove your identity. If your wireless LAN uses username and password−based authentication, you should make sure that you type them correctly.

• VPN−Related Problems

Using VPNs can become quite cumbersome if the instructions for VPN setup are not properly provided to the VPN users. You should make sure that all users fully understand the purpose and procedure of using VPNs, as VPNs require configuration of various cryptographic protocols and algorithms, which might not be the most trivial things to understand.

• Network Design and IP Address Assignment

If an access point or a client adapter becomes inaccessible on the network, you need to ensure that another computer in the LAN is not sharing the IP address.

If you have multiple LANs, you need to further ensure that the network is properly designed and correct gateway information is configured in all appropriate places, for example routers and network adapters.