This afternoon i was checking the reason why my Ubuntu VM image cannot connect to the internet and i found the IPv6 setting in ifconfig. Since i was in bad mood, i wanted to disable the IPv6 in Ubuntu. (Actually the connection problem was not related to it)
1. Edit the /etc/modprobe.d/aliases
2. Change the the alias net-pf-10 ipv6 to alias net-pf-10 off ipv6
3. Reboot and the IPv6 information will be get out from ifconfig
Reference: Ubuntu Geek
Eureka! 
I don’t have that file (running ebuntu based on ubuntu). Did you create it? Also what version of Ubuntu you running?]
Cheers
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The Ubuntu version is 8.04 and i didn’t create the /etc/modprobe.d/aliases file.
Do u have a file called /etc/modprobe.d/blacklist? If yes, add a line blacklist ipv6 to that file and reboot.
You can also refer to this url How-To: Disable IPV6 to speed up Internet. There are so many tricks on how to disable IPv6 on Ubuntu. =)
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ipv6 is the way forward. I have successfully sped up certain areas of internet access by using ipv6 through a tunnel broker.
From Windows XP SP3 onwards, native ipv6 has become the first method of trying to establish a connection. Problems actually come from not having the native connection, not from problems in the kernel any more. In fact torrent downloads are faster, and I believe it’s due to teredo being activated as default in Windows Vista and above, and the connection being used by certain Bit Torrent clients.
The only problem I’m having is certain wireless drivers not appearing to accept the router advertising daemon requests.
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i think we still have to wait for a long time to see the rise of ipv6. i have read ur blog and seems you are very interested in ipv6. keep up your work. =)
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