When Murphy's Law meets Wi-Fi don't panic. Here's how to troubleshoot your wireless connection.
Whether this is the case, or you just want to be more self sufficient on the road, this article will guide you through steps you can take to troubleshoot connection problems. Depending on the problem, you might not always be able to connect without the help of a system administrator, but at least you'll understand why you can't connect. Plus, understanding how the connection works will make that dreaded tech support call shorter and less painful.
Meet your new best friend: ping
This article details the flow chart shown in figure 1. The first step to diagnosing wireless problems is to figure out where the failure is occurring. The basic communication language for the Internet is TCP/IP, so that's where you want to start. For basic TCP/IP troubleshooting, you use your trusty friend, the ping utility.
[FIGURE 1 OMITTED]
Ping is a neat program that can probe remote machines. According to legend, the tool is named after the sound that sonar makes when trying to detect other vessels in the ocean. As such, you use this tool to "ping" a remote host (this could be another client, a server, etc.) to understand if it is reachable (if your computer can "see" it) and how far away it is. Knowing how tar away the remote host is helps you understand why your connection might be slow. Using ping is like saying, "Is there anybody out there?" You send a packet and hope a reply comes back. The reply will include information to tell you how long the trip took.
You can access the ping utility by opening a DOS prompt. There are a couple of ways to do this, but the easiest is to click on your Start menu > Programs > MSDOS Prompt. You can also try Start > Run and type cmd or command, depending on your version of Windows, and click on OK. When you have a DOS prompt open, type ping and press Enter to get information about the commands you can use with this useful tool.
The first link you want to use ping to test is between the wireless client and the access point (AP). If you don't know the IP address of your AP, re-open the DOS prompt and type ipconfig and look for information on the default gateway.
TIP: If you're using an older version of Windows (such as Windows 98 or 95) you can use the graphical interface tool for ipconfig by clicking on Start > Run and typing winipcfg. You still have to go back to the DOS prompt to ping the access point though. Windows 95 only supports winipcfg. Windows 98 supports both ipconfig and winipcfg. Windows NT4, 2000 and XP only support ipconfig.
If you don't see a default gateway, your wireless card might not be associated with an Access Point. See the section wireless association for more information.
In figure 2, you can see that my access point's IP address is 10.0.0.1. You can ping your access point by typing ping followed by your access point's IE In my case:
[FIGURE 2 OMITTED]
When I ping my AP, I see the information shown in figure 3.
[FIGURE 3 OMITTED]
If you can ping your AP, you know the link between your client and the AP (i.e., your wireless link) is OK. See the section on wireless association to find out what to do if you can't ping your AP.
Next, you want to check that the link between the AP and the Internet is working. You do this by pinging a destination beyond the AP. I recommend pinging an actual IP address first, and then trying to ping a hostname. For example, the hostname http://www.ucsd.edu resolves to the IP address: 18.104.22.168. So, try to ping 22.214.171.124 first. If that works, try to ping www.ucsd.edu. (You do not type in the the http:// portion of the URL.)
The point of pinging the IP address first is to isolate a domain name system (DNS) problem. DNS is the service that translates a hostname to an IP address. Therefore, if you can ping the IP address, but you can't ping the DNS name, the problem has nothing to do with your wireless link. It's probably related to your DNS service or configuration. Time to call a system administrator.
If any of your ping tests say "Request timed out," the ping packet never came back and the destination host isn't responding. The problem could be anywhere between your machine and the host you're trying to ping. If you can ping a hostname (ping www.ucsd.edu), your connection is operating normally.
Now that you've preliminarily identified the failure, it's time to dig a little deeper to try and find its source. Keep in mind that if you can ping the AP, but you can't ping a Web site, your client is configured properly and the failure is probably beyond your control. If the AP can't "see" the Internet, it's time to contact your system administrator and notify them of the failure.
On the other hand, if you can't ping your AP, the problem lies between you and the access point. It's possible the AP has failed or lost power, but more than likely, your client is configured incorrectly.
For a wireless connection to work, a client must first associate with an AP, then obtain an IP address. To associate, a client and an AP must have the same Service Set ID (SSID) defined in their configuration screens. They must also have the same WEP key defined, if WEP is enabled. I won't get into the details of WEP here, other than to say it's a wireless security mechanism. (Wi-Fi Protected Access (WPA) is emerging as a way to address these issues and is an alternative to WEP. You can find more information on WPA in John Eder's article on page 26.)
Each wireless card manufacturer includes a different tool to set up configuration parameters; but, at the end of the day, they're all trying to help you achieve the same thing: Configure your settings (SSID, WEP, and other parameters) so you can connect. Also, each too] a]so displays information about the strength of the wireless signal. If no wireless signal is detected, you should contact a system administrator right away. If you changed your SSID settings (say, to connect your laptop at a Borders bookstore hot spot), you must remember to change your settings back to your company's SSID. Also, some APs will work with clients that have set their SSID to "any." In this case, the client connects to the AP with the strongest signal. For more information about configuring your particular card, review your user guide. The following section gives URLs to the users guides for some popular wireless cards.
I realize there's a problem with giving you the URL for your card s instructions if you don t have a connection through which to download them. Therefore, I strongly suggest downloading the documentation and either printing it to carry with you when you travel, or storing it on your hard drive before you hit the road.
If you have a Linksys PC Card:
WPC11, v2.5: ftp://ftp.linksys.com/pdf/wpc11V25ug.pdf
WPC11, v3.0: ftp://ftp.linksys.com/pdf/wpc11v3ug.pdf
If you have a D-Link PC Card:
If you have an SMC PC Card: SMC2632W:
If you have a Cisco PC Card: 340 Series:
Double-check the SSID
Assuming the AP is working properly, you should use your client configuration tools to ensure the SSID is set properly. Some wireless cards will include tools to tell you about the SSIDs it detects in the area. You can then choose which SSID you wish to associate with.
The WEP key should already be set. This information (which is kind of like an encryption "password") is generally known only by the system administrator who initially configured the wireless network.
In Infrastructure mode, you don't have to define a "channel." The client will send out probe requests on all channels to find the AP with the SSID you've defined. You only have to worry about the channel setting in peer-to-peer mode, sometimes called "ad hoc networking."
Microsoft Windows XP is the first 802.11-aware operating system. As such, you can configure your wireless card through the operating system instead of using the proprietary tools that ships with each individual wireless card.
In your system tray, right-click on your network icon (the icon that looks like two small monitors) and you will see a menu with options to disable, status, repair, etc. Click on View Available Wireless Networks option (figure 4). This gives you a list of available networks you can connect to (figure 5).
[FIGURES 4-5 OMITTED]
Get an IP address
Now that you've established a wireless link by associating with an access point, the next step is to ensure you have an IP address. Most wireless (and wired) networks use a service called Dynamic Host Configuration Protocol (DHCP) to dynamically assign an IP address. Because DHCP-assigned IP addresses are time limited, you will sometimes hear people say that you have "leased an IP using DHCP." You can release and renew DHCP leases, kind of like checking a book out of the library. This article assumes that DHCP is in place. (If your network uses static addressing then releasing and renewing does not apply.)
If you're sure that your client is associated with an AP, but you still can t ping your AP, open a DOS prompt. If you reusing Windows NT4, 2000 or XP, type ipconfig/release and press Enter. Next, type ipconfig/renew and press Enter. If you're using Windows 98, the commands are slightly different: ipconfig/release_all and ipconfig/renew_all. For Windows 95, use the winipcfg tool and click the Release All and Renew All buttons. After your machine releases and renews your IP address, type ipconfig and press Enter and you should see your new IP information. Note that there will be an entry for each interface (ipconfig can release and renew interfaces individually, but to keep things simple, I suggest just releasing and renewing all of them), if you have multiple interfaces and want more information about each one, type the ipconfig /all command. If it scrolls by too fast, try:
ipconfig/all | more
When you release your DHCP lease, you get a screen that looks like figure 6.
[FIGURE 6 OMITTED]
Renewing your DHCP lease looks like the screen shown in figure 7 (my WLAN card is on interface 2).
[FIGURE 7 OMITTED]
Windows arbitrarily assigns an IP address in the 169.254.x.x range if it's unsuccessful in trying to lease an IP address using DHCP. In the example shown in figure 7, DHCP successfully configured interface 2. After you have a valid IP address, try pinging your AP again. If that works, try to ping a valid IP address on the Internet (e.g., 126.96.36.199). Finally, if that works, try to ping a valid hostname on the Internet (e.g., http://www.ucsd.edu). If you can ping a host name on the Internet successfully, but if you can't get your browser or e-mail client to connect, you're probably dealing with an application-specific issue and not a wireless problem.
If all else fails ...
Wireless networks give workers a new sense of freedom and enable workflow productivity gains that aren't possible in a wired environment. However, sometimes wireless problems occur and we're forced to go back to the "old" ways of chaining ourselves to the network. Chances are that your laptop still has a standard Ethernet RJ-45 jack. Try plugging the laptop into a wired Ethernet port and see if this resolves your problem (if you can still find a cable).
There are many conditions that could be temporarily affecting your network. For example, interference from other wireless networks, microwave ovens, cordless phones and even certain weather conditions can affect RF signals and Wi-Fi performance. The problem might even be as simple as too many users trying to connect at once. Poor site surveys and site' planning can result in temperamental wireless networks that fail intermittently. If necessary, you can always "go wired" for a while and try the wireless connection again later. Sure, it's a little like going back to the days before running water and indoor plumbing, but primitive as it may be, sometimes you just have to get your work done.
On the other hand, maybe it's time for a Starbucks run? I hear they have a pretty good wireless network.
MOBILE BUSINESS BENEFITS
It used to be that business people only had to deal with business Issues. You know, things like tracking budget and sales figures, schmoozing clients, closing deals, working on your golf swing ... But, technology is no longer the sole domain of IT and you have one more title to add to your job description: propellerhead. Technology--In this case, an Internet connection--is a business tool. If you're a less then tech-savvy business user, you can easily find yourself stranded and frustrated trying to deal with wireless connection problems. This tutorial puts wireless networking in basic terms and will help you get connected.
It's important to understand that wireless communication happens in layers. Networking works in building blocks; one layer rests on top of another. The Open System Interconnection (OSI) model is a framework that defines networking protocols in seven layers. Wi-Fi is defined on the boom two layers; however, when diagnosing Wi-Fi problems, you're also interested in the third layer. Layers 1, 2, and 3 are the Physical, Data Link, and Network layer, respectively.
LAYER 1: Physical
For wireless communication, this layer defines things like the radio frequency, power outputs, and modulation techniques. The 802.11 specification includes three physical layer protocol definitions; the one you're most interested in for Wi-Fi is the Direct Sequence Spread Sprectrum (DSSS). The other two supported protocols at the physical layer are Frequency Hopping Spread Spectrum (FHSS) and Infrared (IR).
LAYER 2: Data Link
The second layer is concerned with everything on the local "wire" or network. It communicates using Media Access Control (MAC) addresses, which are 48-bit hardware addresses (usually represented by 12 hex characters printed on the back of the card). The MAC address breaks down into two parts. The first 24 bits represent the hardware vendor (e.g., Linksys, Cisco, or whoever made your network interface card). The second 24 bits are a unique number assigned by the hardware vendor. In theory, combining these two values gives you a globally unique value (i.e., the MAC address). Layer 2 defines the wireless topology modes. This includes details on how wireless "association" works.
LAYER 3: Network
This layer gets packets from one network to another and communicates using IP addresses. Layer 3 is beyond the scope of the 802.11 protocol; however, I include it in this article because it is an essential part of troubleshooting your wireless connection.
Lee Barken, CISSP, CCNA, MCP, has been in the IT industry since 1987. Lee has worked as an IT consultant and network security specialist for Ernst & Young's Information Technology Risk Management (ITRM) practice and KPMG's Risk and Advisory Services (RAS) practice. Lee is the co-founder of the San Diego Wireless Users Group (http://www.sdwug.org) and writes and speaks on the topic of wireless LAN technology and security. He teaches the "WLAN Deployment and Security" class for University of California at San Diego (UCSD) Extension and is writing a comprehensive book on wireless security. firstname.lastname@example.org.
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|Title Annotation:||Wireless Web|
|Publication:||Mobile Business Advisor|
|Date:||Feb 1, 2003|
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