Is "connnection sharing" necessary in windows-7 host to allow VirtualBox's Ubuntu guest connect to internet through (default) NAT interface? My network administrator (on the machine at work) has disabled "conenction sharing" and some answers in threads( http://serverfault.com/questions/225155/virtualbox-how-to-set-up-networking-so-both-host-and-guest-can-access-internet) suggest it is necessary.
Note It seems I face "proxy issues" in the cocorporation where I work. We are behind some kind of http proxy so my browser works but (probably) no other connections are allowed.
Note2 Connection sharing has nothing to do with my problem. I solved it after investigating proxy settings: it turned out that I should set http_proxy environment variable on guest Ubuntu (https://help.ubuntu.com/community/AptGet/Howto) and my problem is immediately solved.