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I have a PC with a LAN connection and a WLAN connection like this:

LAN: Local network, several PCs and an old DSL-modem that is not connected to the internet but only used as a DHCP server, the IP comes from that DHCP server.

WLAN: a DSL router connected to the internet, IP comes from DSL-router.

If I deactivate the LAN, I can connect to the internet through the DSL-router as usual.

If I activate the LAN, it seems that any internet request is routed to the LAN and therefore I don't have an internet connection. A ping to a website shows that the LAN-DSL-DHCP-device answers that it cannot connect to the website.
I guess that's because there is a device in the LAN that would be able to connect to the internet?

How can I route internet requests towards the WLAN connection, even if the LAN is active?

And how does Windows decide which network connection to use for an internet connection?

(one more note: everything worked before the LAN-DHCP device was added)

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up vote 1 down vote accepted

Look at the advanced option within ncpa.cpl (Network interfaces) and prioritise the WAN interface over the LAN one. Or maybe removing the Default Gateway on the LAN interface may work. (But you will lose DHCP)

You can print the routes in a cmd with : route PRINT command. You should see something like :

Network destination   Netmask        Gateway           Interface        Metric          10

Saying that all packet to networks that did not match an address for other routes are directed to the Gateway mentioned here (by using the interface mentioned).

You can alter the routing table with the route command as well.

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Thank you! I had two entries with MASK, one to the DSL-router and one to the LAN. After removing both (seems one can only remove all at once) and adding just one pointing to the DSL-router, it now works fine. – Holgerwa Mar 10 '11 at 12:01
In fact you should be able to distinguish between two route, maybe with more parameters don't remember for windows. Good Luck. – M'vy Mar 10 '11 at 12:29

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