You can't rely on the Qt API on this one.
You better use the platform API:

Windows:
http://www.codeproject.com/internet/NetCnfgVersion2.asp
http://www.codeproject.com/internet/getmac.asp

Linux:
http://kasperd.net/~kasperd/comp.os....lopment.faq#IP
See paragraph 29.

Mac:
Search http://developer.apple.com


Regards