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Troubleshooting Q&A - December 4, 2003 Overcoming Wireless Network Configuration Obstacles Any number of problems can pop up when attempting to properly configure a wireless network. This week's Q&A provides solutions for some of the more common configuration issues. By Ron Pacchiano Q. I just purchased a new laptop computer to replace my outdated desktop. Instead of throwing out the old PC I decided I would clean it up and give it to my kids to use. I have a high-speed cable modem in the house that I use for Internet access, which was previously connected directly to my PC. Now that we have two computers in the house, I would like to find a way to share the cable modem. So on a recent trip to Costco I purchased a D-Link wireless router and PC card combo pack. The nice thing about this router is that it works with both wired and wireless networks. I connected the desktop directly to the router via an Ethernet cable and installed the wireless PC Card on my laptop. The desktop is now working perfectly with the wireless router, but I can’t seem to get my laptop online. After examining the TCP/IP settings of both PCs, I think I might have discovered the problem. It appears that my laptop is using an IP address of 169.254.255.2, while my desktop is using an address of 192.168.0.2. I double-checked my router settings, and the DHCP server is supposed to be assigning IP addresses beginning with 192. I am at a loss to explain how the laptop is getting the 169.x.x.x IP address. I’m concerned that I might be connecting to someone else’s wireless network, because if I connect my laptop to the router using an Ethernet cable, everything works fine. What do you think the problem is, and how do I find out where this 169.x.x.x address is coming from? Thank you for your assistance. A. The cause of your problem isn’t as ominous as you might think. Most importantly, the problem has nothing to do with you connecting to someone else’s wireless network; rather, it has to do with the fact that your wireless NIC is not communicating properly with your router. As any regular reader of this column can attest to, this is a very common problem. In all of the times I’ve answered this question in the past, I’ve never really explained what mechanism is responsible for generating the 169.x.x.x IP address. This is actually the result of a feature built into most Windows-based operating systems called APIPA. APIPA, or Automatic Private IP Addressing, enables a computer to automatically assign itself an IP address when there is no DHCP server available to perform that function. You see, when a DHCP client boots up, it first looks for a DHCP server in order to obtain an IP address and subnet mask. If the client is unable to find the information, it uses APIPA to automatically configure itself with an IP address from a specific range that has been reserved especially for Microsoft by the Internet Assigned Numbers Authority (IANA). That IP address range is 169.254.0.1 through 169.254.255.254. The client also configures itself with a default class B subnet mask of 255.255.0.0. The APIPA service will also continuously check for the presence of a DHCP server (every five minutes, according to Microsoft). If it detects a DHCP server on the network, APIPA stops and the DHCP server replaces the APIPA networking addresses with a dynamically assigned address. Diagnosing Wireless Configuration Issues Now that you understand where the 169.254.x.x IP address is coming from and why it has been issued, you also know that your wireless network adapter is not communicating properly with your wireless router (since it’s not receiving a DHCP-assigned IP address). Your PC is working when used with the Ethernet cable, so I think it’s safe to assume that your TCP/IP protocol has been installed and configured correctly. Therefore it must be a problem with the way you configured your wireless network. Any number of variables could be causing this situation. Let’s take a look at few of the more common ones. One of the biggest hurdles to getting a WLAN configured properly is WEP/WPA encryption. I know you want your network to be secure, and I would never tell you to run your network without encryption, but during the configuration process it is significantly easier to get things up and running with encryption disabled. So the first thing I would recommend doing is disabling WEP/WPA. Next, you should verify that both the router and the PC card are using the same SSID name. The SSID, or Service Set Identifier, is a unique 32-character identifier that differentiates one wireless LAN (WLAN) from another. All devices attempting to connect to a specific WLAN must use the same SSID. The SSID’s function is similar to that of a wired network’s Workgroup or Domain name, and a workstation will not be permitted to wirelessly connect to the network unless it can provide this unique identifier. After that, you should confirm that both devices are set to broadcast on the same channel. There are 11 channels available, and I believe 6 is the default channel for most 802.11b products. It doesn’t really matter which one you use, as long as they match. Wireless networks also operate in one of two modes: Infrastructure or AdHoc. Your wireless adapter should be running in Infrastructure mode. In AdHoc mode, a wireless client can communicate directly with other wireless clients without the need for an access point or router. In Infrastructure mode, an access point or router is needed for a wireless client to gain access to the wireless LAN or WLAN. As a result, whenever there’s a need for wirelessly sharing a cable modem or DSL connection, Infrastructure mode needs to be used. Additionally, you might want to keep the laptop in the same room as the router, at least during the initial configuration, to minimize potential interference from concrete walls or steel beams. Once your wireless adapter and the wireless router are configured correctly, the DHCP service will automatically assign it a suitable IP addresses. With the wireless network successfully configured, we can now enable WEP. It is very important to remember that there are many different levels of encryption available, with the most common being 64- and 128-bit. Some products, like those from D-Link, can even support 256-bit encryption. I would recommend that you use the highest level of encryption that your hardware can support — in this case, 256-bit. In order for encrypted devices to communicate with each other, they need to share a common key. Key types are typically made up of either HEX (Hexadecimal) or ASCII (American Standard Code for Information Interchange) characters. Both the wireless adapter and the router must be using the same encryption level and the same key type. While this may sound simple enough, it is very easy to mistype a key or change an encryption level, which would completely disable your wireless network, so double-check everything during the configuration process. Remember, don’t assume anything; verify for yourself that all of the required settings are correct. This should be enough information to get you started. Follow these general guidelines, and you should find yourself online in no time. Best of Luck!
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