I Have upgraded from 12.04 to 12.10 and upgrade went smoothly, but after the restart I was not able to access the Internet and unable to ping any Domain like google.com, though i was able to access my wireless router.
After investigating i found out that /etc/resolv.conf contains Loopback address(127.0.0.1) I updated this file with google public DNS address (8.8.8.8) and tried to restart Network Manager and then my system got struck eventually I have to reboot it.After Rebooting I was able to access internet , but problem doesn't get over yet now when ever I switch the network DNS Network doesn't get change with network( i am on DHCP) , which i need to change manually every time.
I understand that the loop back address was correct /etc/resolv.conf as Network manger should handle the DNS Server but unfortunately it didn't work out for me.