An understanding of wireless LAN (WLAN) client and WLAN access point (AP) communication mechanisms is critical
to anyone attempting to initially connect or troubleshoot a WLAN connection. In this article, I discuss how to troubleshoot WLAN client connectivity issues.
There are several features of the WLAN client that require configuration in order to connect to a wireless AP and to transmit data. These can include SSID, IP addressing, security and channel configuration parameters. Basically, the WLAN client configuration will have to meet the configuration that has been set up on the AP. In most cases, an admin configuring a WLAN for office users or the user setting up a WLAN in a home office will be configuring the access point and can therefore match the client configuration settings and AP settings easily. However, most of the WLAN client issues I see relate to users who have new WLAN cards or embedded WLAN cards.
As I said above, in order to connect to an AP, the client and AP must match in their configuration. The first thing that you want to ensure is that the client is configured properly. The following are the basic configuration parameters that must be met:
- Service set identifier (SSID) setting: This is a unique identifier that distinguishes one WLAN from another. This used to be the only security enabled for a WLAN, in that only clients that were configured with the proper SSID could connect to the WLAN. In most cases the SSID is broadcast so that your WLAN card will identify it automatically.
- Channel settings: APs have multiple channels on which they broadcast their signals. If there are multiple APs in the area, they will need to transmit on different channels to prevent interference. This means that you may use channel 1 at home but may need to use channel 6 or 11 at a Wi-Fi hotspot or hotel. Channels 1, 6 and 11 are for 802.11b WLAN networks. Again, in most cases this information is broadcast and the WLAN card will detect it automatically.
- Security settings: Unlike the SSID and channel settings, this information has to be provided to you. The security settings are in place in order to prevent unauthorized access.
- IP addressing: An IP address, subnet mask, and default gateway are needed to transmit data over a WLAN connection. The three settings above relate to physically connecting the laptop/PC to the AP. The IP address is needed to communicate over that connection. Once connected, the AP has the ability to automatically assign this information to the WLAN client, but if the AP is not set up to do this, the client will need to be manually configured with this information. In addition, the information will have to be provided to you.
Troubleshooting the client
Once you have looked at all the areas that need to be configured, the real focus is how you configure/troubleshoot the client. Let's consider the client device for a minute. If you are the person who installs the WLAN card, make sure that you install the GUI capabilities of the WLAN card. This is basically a front end that allows you to view available WLAN networks and configure the information on them. In most cases, the GUI will show available networks (the actual SSID) and the channels that they are broadcasting. Just double-click the available network and see whether your card connects. If there is a symbol beside the network name that looks like a lock, it means the AP is configured with security mechanisms and you will have to get this information from the AP administrator to connect. Once connected (the GUI will show that you are connected) you can ascertain whether or not you have been assigned an IP address by doing the following:
- Click on "start"
- Click on "run"
- In the command line, type "cmd" to pull up a DOS window
- In the DOS window, type "ipconfig"
- If you have been assigned the appropriate IP Addressing information, you will see something similar to the following:
Microsoft Windows XP [Version 5.1.2600] (C) Copyright 1985-2001 Microsoft Corp. C:\Documents and Settings\Robbie Harrell>ipconfig Windows IP Configuration Ethernet adapter Wireless Network Connection 3: Connection-specific DNS Suffix . : IP Address. . . . . . . . . . . . : 192.168.0.2 Subnet Mask . . . . . . . . . . . : 255.255.255.0 Default Gateway . . . . . . . . . : 192.168.0.1
- Make sure the information is applied to the wireless network connection.
This is really straightforward. However, many new laptops are shipping with Intel Centrino Mobile network adapters already installed in the laptop. This means that you did not install a WLAN card, it was just there. The only way to configure the embedded WLAN card is via the Windows software installed on your PC. Windows software will walk you through the setup and configuration of the WLAN card, but I can attest from experience that it is really confusing. In addition, if you have to modify these settings, it can be very cumbersome. Therefore, the recommendation is to download and install the drivers that include the GUI for the embedded Centrino WLAN NIC. Here is how that is done:
- Click on "start"
- Click on "control panel"
- Click on "network connections"
There are several different network connections you may be able to see. One may be a LAN connection, but what you are looking for is the WLAN connection. The screen will show the connection name, type, status, device name, or some variation of these. The key information is the device name. On my Dell laptop, I have the Intel PRO/Wireless 2915ABG network connection. When I first got my new laptop, I could not configure this adapter, so I downloaded the drivers from Dell and installed them. Now I have a GUI and do not have to utilize Microsoft's mechanisms for configuring the adapter.
That's it. Installing the GUI and knowing how to validate and configure the SSID, channel, security and IP address settings will solve 99% of the client issues associated with WLAN connectivity. Most of the other issues are related to performance of the RF environment and the back-end infrastructure supporting the WLAN network, all of which cannot be addressed by the end user.
Robbie Harrell (CCIE#3873) is the National Practice Lead for Advanced Infrastructure Solutions for SBC Communications. He has more than 10 years of experience providing strategic, business and technical consulting services. Robbie lives in Atlanta and is a graduate of Clemson University. His background includes positions as a Principal Architect at International Network Services, Lucent, Frontway and Callisma.