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Concurrent connection issues: Get wireless and wired to play nice

Wireless expert, Lisa Phifer explores concurrent connection issues and remedies with a printer requiring a wired connection plugged into a computer with a wireless connection to the Internet.

I'm trying to connect a printer that can only use an Ethernet connection (directly wired from printer to computer)....

When I plug in the Ethernet, it turns off my wireless connection to the Internet. How can I plug my printer into my Windows 7 computer without it disabling my wireless connection to the Internet?

Some companies explicitly ban concurrent wireless and wired connections to prevent traffic from being bridged accidentally, creating an unprotected back door into a corporate network. If you're using a computer supplied by your employer, ask your IT administrator or helpdesk whether they might have installed a security agent or configured policies that could be preventing concurrent use of wireless (Wi-Fi) and wired (Ethernet) connections.

If that's not the case, you may be experiencing an unintentional consequence of having two active connections to the same network. Suppose both your wireless and wired connections receive an address from the 192.16.1.x subnet. By default, all traffic is automatically routed through the connection with a faster data rate. So, if you're using 10/100 Ethernet (max data rate 100 Mbps) and 802.11g Wi-Fi (max data rate 54 Mbps), your Ethernet connection will "win" and all traffic will be routed over Ethernet instead of Wi-Fi. But if you were using 2x2 MIMO 802.11n Wi-Fi (max data rate 300 Mbps), your Wi-Fi connection would "win" and receive all traffic.

To determine whether this is your problem, open a Command Window and type "route print" – first, when only Wi-Fi is connected, then when only Ethernet is connected, and then when both are connected. Compare the "Interfaces" listed with Ethernet-only and Wi-Fi-only to determine which is wired and which is wireless, and look at the column labeled "Metric." When both connections are active, does your Ethernet have a lower metric than your Wi-Fi?

If this seems to be your problem, I suggest moving your printer and Ethernet into a different subnet than your Wi-Fi. This can be done by manually configuring IP addresses for your printer and your computer's Ethernet connection – for example, give them both an address from 192.168.2.x instead of 192.168.1.x, but do not set default gateway. This is a good permanent solution if your printer is directly cabled to your computer's Ethernet port, using a cross-over cable – changing their IP addresses won't affect any other device, and your computer will no longer try to use Ethernet as a default route to the Internet.

However, if you want the printer to be reachable by other wireless users, you must find another solution, such as plugging the printer into a port on your wireless router or turning on bridging between your computer's Ethernet and Wi-Fi connections. For the latter, see http://windows.microsoft.com/en-US/windows-vista/Create-a-network-bridge.

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