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Using DHCP on a WLAN

Solving problems with wireless cards that can't receive an IP Address from a router; and just what is a home network router good for, anyway?

By Joe and Ron of Neighborhood Techs

Q. I have a wireless USB network adapter which is configured for DHCP. For some reason however, the wireless router can not assign an IP address to it. What do I need to do to resolve this problem?

A. Your wireless USB network card is configured to automatically receive an IP address from the wireless router's Dynamic Host Configuration Protocol (DHCP) server, yet it is not receiving one. I think your wireless NIC probably a 169 IP address assigned to it. You can verify this on a Windows 9x/ME system by clicking on the Start Menu and selecting Run, then typing WINIPCFG. In Windows 2000/XP, go to Start, select Run, then open a DOS command line window by typing CMD. At the command line, type IPCONFIG.

An IP address that begins with a 169 typically means that the NIC can not communicate with the DHCP server. This would indicate to me that the problem is related to a wireless network that just hasn't been configured correctly.

Don't be discouraged though. Wireless networks can be very complicated to setup, particularly if you're dealing with encryption and products from different vendors. Any number of variables can keep you workstations from talking with each other. Some of the more common problems involve the following:

Verify that your router and your workstation are using the same Service Set Identifier (SSID) descriptions. This is a unique identifier up to 32-characters long that is attached to the header of packets sent over a WLAN. It acts as a password when a mobile device tries to connect to the wireless network. The SSID also differentiates one WLAN from another, so all access points and all devices attempting to connect to a specific WLAN must use the same SSID. A workstation will not be permitted to connect to the network unless it can provide this unique identifier.

When you're experiencing conductivity problems it is always best to keep things simple. Your router could be set for either 64 or 128-bit encryption, while other manufactures use 40 or 256-bit encryption. For now, disable any WEP encryption -- it can one of the most convoluted components of a wireless network.

Successfully turning on encryption also includes the use of a shared key. A HEX key is most common, but other formats are also used. This key identifies the workstation to the router as a trusted member of this network. Different manufactures can implement this key technology in ways that might prevent them from working correctly with other vendor's products. So attention to detail is going to be the key to a successful installation.

Make sure the router and the NIC are configured to use the same communications channel. There are normally 11 channels and the default channel can vary by vendor. You might also want to confirm that the router has DHCP services enabled and an IP address pool configured. If not, the NIC won't be able to pick up an IP address. I have run across a few access points that offered DHCP services but did not assign all of the needed IP information to the NIC. For example, one product would assign a workstation an IP address, subnet mask and gateway, but would not provide it with any Domain Name System (DNS) information. As a result, I could connect to the network, but not browse the Web.

The point is,…don't assume anything. Verify for yourself that all of the required settings are being received by the workstation.

Lastly you might want to keep the system your trying to configure in the same room as the router, at least during the initial configuration, to minimize potential interference from concrete walls or steel beams.

Once you get the workstation and the wireless NIC talking to each other verify that your workstation is part of the same domain or workgroup as the rest of the network systems. If not, you won't be able to see or access any other systems on the network. This should be enough information to get you started.

Q. I'm currently using the Ethernet connection on my desktop to link to my laptop computer. I'd like to add a broadband connection to my systems but I'm not sure how I would go about connecting them as I have no more Ethernet ports available. How can I give both of these systems access to the Internet?

A. The easiest thing to do would be to purchase a low cost router, like the Belkin 4-Port Cable/DSL Gateway Router. This router sells on Buy.com for under $80 and not only allows you to share an Internet connection with multiple PCs, but provides your network with NAT firewall security to help protect your home or office network from would-be hackers. I highly recommend using a firewall with any type of broadband technology. Using this router you could have both machines surfing the Web in no more then 5 minutes.

Other options available would be to create a multi-homed system by adding a second NIC card to your desktop. This would allow you to use one connection for Internet WAN traffic and the other for local LAN traffic. This is a much more complicated procedure however and could prove to be VERY problematic. The Microsoft Knowledge Base can provide you with information on how to do this as it is just too complicated to get into here. My advice: Save yourself the headache and just invest in the router.

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