At the beginning of this year, the IT people in my firm installed a new proxy server. How nice, I thought to myself, because the old one wasn't able to pass through a connection to FTP servers outside our intranet. But I had to notice that now nothing related to the internet worked!
After some reserach, I arrived at the conclusion that the new proxy has a new authorisation method called NTLM. Yes, Windows supports that because they developed this authentification method by themselves. But except for Internet Explorer, internet access from Macintosh no longer works with NTLM. Another hint discussed something like this before, but the tips given in this hint were no solution for my problem.
After some more research, I found Authoxy. It's a "local proxy" in form of a System Preferences pane. All you have to do is to download Authoxy, install the package, and open the Network settings in your System Preferences. Now, instead of the IP address of the proxy of your firm, enter 127.0.0.1t (your localhost) and use port 8080.
Then open the Authoxy Prefence pane, enter the IP and port of the "real" proxy server. In the next tab, enter the domain name of the proxy (maybe your network administrator can help; otherwise, when making a connection to the internet via Internet Explorer, it's shown below username and password when authentificating). Now start Authoxy.
I also added the installed "start Authoxy" application to the Startup Items of every user, and now have my internet access back.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20050107133741467