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I am using Ubuntu 10.04 (installed using Wubi in Windows 7) and when I change my proxy settings to no proxy (without any proxy server), I am unable to access any page (using Firefox or Google Chrome) on the internet except for pages on our local intranet (internal to IIT Kanpur)

I am a student of Indian Institute of Technology Kanpur (IIT Kanpur). When I change my domain name servers from my default IITK ones (mentioned below) to Google Public DNS (8.8.8.8, 8.8.4.4), I am able to access the internet normally.
Default (IIT Kanpur recommended) settings are:
DNS - 172.31.1.1, 172.31.1.130

We are supposed to Authenticate our identity before accessing pages other than the internal ones, say to access Google (IIT Kanpur uses a using Fortigate Firewall for this purpose) if we are using no proxy server. And if wish, we can also use proxy servers (like bsnlproxy.iitk.ac.in or ironport1.iitk.ac.in) for accessing the internet.

Also, whenever I start using Ubuntu initially after installation (happened to me with Ubuntu 12.04 also), I can access the internet normally for few days after which I notice that one by one all the websites are inaccessible via no-proxy. I am puzzled by this issue

When I started using Ubuntu after installation using Wubi(Windows Ubuntu Installer) from Windows 7, I noticed that I could use authenticate my identity and use the internet normally for a few days. Afterwards, I started noticing that I am unable to access certain websites like Wikipedia but could access Google normally, and soon after this, I was unable to access any website outside our IIT Kanpur network even after Authenticating the firewall (Page Not Found Error). This surprised me. But I also noticed that I could always access the internet normally using any one of the proxy servers provided by IIT Kanpur.

Please note that I never face this problem when using the no proxy settings in my actual operating system i.e. Windows 7.

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Please comment if anything is not clear or information is incomplete. I can provide any necessary details if needed. –  user2001116 Jan 23 '13 at 16:53
    
Are you inside the university network when you are trying it? Can you try to open a terminal and enter host askubuntu.com 172.31.1.1 and host INTERNAL_HOST 172.31.1.1 where INTERNAL_HOST is a hostname inside your network? Do both commands work properly? –  qbi Feb 5 '13 at 7:06
    
@qbi Yes, i am inside my university network all the time. –  user2001116 Feb 6 '13 at 13:06
    
@qbi No, the first command host askubuntu.com 172.31.1.1 is NOT working properly. But the latter host cse.iitk.ac.in 172.31.1.1 returns a valid IP address –  user2001116 Feb 6 '13 at 13:18
    
For the host askubuntu.com 172.31.1.1, no Aliases are printed. –  user2001116 Feb 6 '13 at 13:27

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