internet access problem in 12.04

Solution 1:

This problem has arised for me after using Cisco AnyConnect VPN Client. For some reason the file contained information of the network I was VPN'ing into. I simply removed the file and everything worked for me.

Solution 2:

May not work for everyone, but I solved this in 12.04 by going to "Edit Connections"(right click on your internet connection logo) and unticking the "Require IPv4 for this connection to complete" box. Instant result!

Solution 3:

This has to do with the switch to resolvconf for /etc/resolv.conf management, as described here.

I solved the problem by inserting dns-nameserver and dns-search options into /etc/network/interfaces. I obtained the values required from /etc/resolvconf/resolv.conf.d/original.

I don't know if this is the "best" or "proper" solution, but it resolved (!) the issue for me. I also don't know why this was necessary.