Automatically prefer Ethernet over WLAN

Solution 1:

You can set your laptop to "prefer" the Ethernet connection over the wireless. TechNet has a quick overview:

The short answer is that Windows (Vista, 7, 2008, and I’m pretty sure XP and 2003 does as well) [or should do] this by default. The key here is the network interface metric. When you have more than one default gateway defined [...] then the internet bound packets go out the interface with the lowest metric.

[...] You can, of course, permanently alter your metrics by editing your TCP/IP settings on your network adapter’s advanced settings.

[...] You should know that Vista made a change to how we handle existing sockets – after plugging in, connections will not be switched over, you must re-establish the connection in order to make use of a wired connection. For example, if you’re downloading something from a website and realize that it would go faster by plugging in, you’d have to cancel and start over after plugging in. This is a change from XP and 2003.

For how to change these settings, have a look at this Microsoft KB article.

Solution 2:

The wireless network is not entirely disabled, but windows is already configured to prefer your wired network when available. This happens via the routing table. Your routing table will have an entry for both interfaces, but the metric for routes on the wired interface has a lower default than routes on the wireless, such that the wired network is checked first when evaluating where to send a packet. You can view your routing table by opening a command prompt and entering route print.