Internet does not work well on Ubuntu but does so on Windows

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http://askubuntu.com – I have a dual boot system with Windows7 and Ubuntu 12.04 with wired internet connection. It is configured to automatic DHCP. The internet works perfectly well on Windows. But on Ubuntu, the connection sometimes work, sometimes not. On most occasions, internet doesn't work. The indicator does say 'Connection established". I have tried other distros earlier with the same issue. I don't understand why it works well in Windows and not on Ubuntu. Please help. (HowTos)