Troubleshooting Wireless Networks
Individuals who must take care of wireless networks may be inclined to view them as entirely different from wired networks. But any time you have to kick formal problem-solving methods into gear on wireless networks, you can’t help but notice that troubleshooting wireless networks and troubleshooting wired networks have more in common than one might think. In fact, aside from the lack of wires linking network nodes together and the presence of some extra gear to make wireless communications possible, there’s really not much difference at all.
That doesn’t mean those differences can be ignored, but it does mean that what networking professionals already know about troubleshooting wired networks transfers rather neatly into troubleshooting their wireless counterparts. That said, wireless transmission and media do have some unique potential sources of trouble that must be investigated, but with the proper tools and techniques they need be neither too difficult nor too expensive to handle.
In a Wireless World, Troubleshooting Basics Remain Unchanged
The basics of troubleshooting any kind of networking trouble might be succinctly stated as “keep eliminating obvious causes until the real cause presents itself.” But understanding what this means requires a systematic approach and real discipline when attempting to identify causes from symptoms and apply the right fixes or workarounds.
In dealing with any networking troubles, viewing the OSI network reference model as a pyramid helps to indicate where the most likely causes of trouble reside. Because a pyramid is big at its base, it rightly indicates that Layer 1 (the physical layer, the realm of hardware, interfaces, cards and connections) is far more likely to harbor problems than Layer 7 (the application layer, the realm of software that usually uses wireless and wired networks with equal facility to perform services or provide data to end users). Layer 2 (data link layer) is where physical addressing (MAC address) and local network membership issues are likely to come up. Layer 3 (network layer) is where network protocol issues like IP address, subnet masks, default gateways, domain name resolution and so forth primarily occur. In fact, it’s no exaggeration to say that system or network administrators primarily shoot trouble in Layers 1 through 3 simply because fixing problems at higher levels is often beyond their capabilities (and to be fair, their interests, as well).
Troubleshooting Basics Revisited
Troubleshooting is a skill that all networking professionals learn by trial and error. But skipping some of the more painful or egregious errors can make your learning somewhat less trying than it might be otherwise. The most important characteristic to cultivate when solving problems is calmness. If you can keep a clear head when things fail or start degrading seriously, you’ll be better able to assess your situation and better equipped to solve whatever problems you discover.
The following set of steps is helpful when troubleshooting networking problems and requires verifying the status of all affected computers or networking components:
- Eliminate user errors: Ask users what they were doing when the problem first appeared. Very often, user errors, unintended configuration changes or attempts to access unavailable resources are reported as network errors. A little research goes a long way here.
- Verify network connections: Check all physical components involved in getting the affected computer(s) onto the (wireless) network. This means interfaces, cables, antennae, PC cards and any other physical components that must function properly for network communications to occur. Ninety percent of all networking problems are solved at this point (which is, of course, at Layer 1). On Windows computers, for example, you can check the Status field in the Network and Dial-up Connections display or look at network icons on the system tray for a red X that indicates a non-working connection. This is where a handheld analyzer can also be handy because it can quickly verify what items are working (or not).
- Verify the status of network interfaces, access points and so forth: If devices are properly interconnected and things should be working, it’s time to use any and all diagnostic information that might be available to make sure all the necessary pieces and parts are working properly. Many wireless interfaces and access points use colored LEDs to communicate problems and normal operation. Use this and other sources of diagnostic information to make sure devices are functioning properly, including access-point tools, operating system networking tools and anything else that’s relevant.
- Restart the computer: Modern servers and desktops include enough software and hardware components to cause occasional hiccups for no good reason. Before digging into full-blown troubleshooting methodology and into the usual suspects for wireless problems covered in the next section, try rebooting an affected machine (unless other checks have pinpointed problems elsewhere).
If these basic steps don’t work, something is probably genuinely amiss. To begin, check into the most frequent culprits when wireless problems emerge.
Wireless Troubleshooting: ‘The Usual Suspects’
Most wireless equipment vendors do a great job of providing troubleshooting support for customers. This often takes the form of a troubleshooting FAQ, a list of frequently asked questions with answers gleaned from tech support’s records in helping with such matters. By presenting your favorite search engine with “wireless troubleshooting” you can find hundreds of such documents, but for best results visit vendor Web sites for the wireless gear you use to find the Q&A that’s most germane to your needs.
My research showed me that the following situations are likely to occur on most wireless networks:
- Check connectivity and interface function: Though this appears prominently in the preceding section, it also appears in every troubleshooting guide around. It therefore bears repeating to make sure that cards or interfaces are working, antennae attached, access points functioning and so forth before seeking more esoteric causes for wireless networking woes. Tools you’d use here would include typical operating system utilities to check on networks, related interfaces, IP address assignments, DHCP and DNS settings and so forth. Again, this is where a wireless handheld analyzer or some other “signal-catcher” (like the NetStumbler kit) will come in handy.
- Check configurations and compatibility: Wireless networks often require that all antennae be set to the same polarity, employ various network IDs and encryption settings and may require other configuration data to establish and maintain proper security and access controls. Each of these settings is a source for a potential mismatch and must therefore be checked at access points and interfaces alike if and when trouble presents itself. Handheld analyzers, access point tools, network interface diagnostics and operating system networking widgets can all help illuminate sources of trouble here.
- Check for signal presence and strength: Each wireless technology uses a part of the wireless communications spectrum to send and receive the signals that make networks work. You’ll want to invest in some kind of portable or handheld wireless analyzer (see “Top Wireless Troubleshooting Tools” for details; for low-budget administrators, try the NetStumbler kit instead), and you should make yourself familiar with your access point vendor’s diagnostics and tools as well. All of these items can help you determine if signals are being sent and received within necessary tolerances. This can lead you into issues related to the distances between senders and receiv