cant connect to internet directly on ubuntu

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http://askubuntu.com – I have dual booted machine windows 7 with ubuntu 12.10. I dont have direct internet access in ubuntu on wired network although direct connection works in windows7. I have to connect through a proxy on ubuntu, which works fine. This is not a ubuntu version related problem as i have been getting it from ubuntu 11.04. I want to know what difference is there in ubuntu and windows 7 which creates such results and how to fix it? (HowTos)