Telstra Mobile Broadband adaptor won't work with ethernet connected

Question

Due to security requirements I'm having to use some rather kludgy workarounds to what should otherwise be a simple issue: I have a scanner connected via ethernet to a computer that our tech support (off-site and third-party) wants to connect to remotely via GoToMeeting. Since we 're not allowed to let him connect using our main network, I'm trying to connect the computer to the internet using a Telstra Mobile Broadband adapator.

This works perfectly fine, as long as the ethernet connection on the computer is disabled. As soon as we enable it, we lose internet access, although the adaptor is still connected. Leaving the ethernet port disabled is not an option, since it's necessary to connect the scanner to the computer.

I've googled around, but the terms are very all-encompassing and I haven't been able to find a match to my situation. I've poked at the various network settings but nothing leaps out at me as a solution to the issue. My guess is that it's trying to use the ethernet to connect. The Mobile Broadband is highest ranked in the Adapators and Bindings section of Network Settings.

Computer is running Windows XP SP3. The Adpator is a MF668A, firmware T03. The ethernet connection is using a fixed IP address, since there is no DHCP server available (it's a direct connection to the scanner). The scanner only allows ethernet connections, there are no other connections possible.

How do I enforce the computer using the mobile adaptor for the internet connection?

Answer 1

Well, this turned out to be a case of not seeing the forest for the trees. It was subnet masking causing a conflict between the networks, with the Mobile adaptor being 10.106.... with a 255.255... and the ethernet being 10.10... with 255.0... After changing the ethernet to 255.255... it was all good again. Putting this answer here in case anyone else forgets to double-check their subnet masks.