apt-get update failure

If running
sudo apt-get updategives following error it's because it's unable to resolve the IP.

Err http://archive.ubuntu.com oneiric Release.gpg
  Unable to connect to archive.ubuntu.com:http: [IP: 91.189.92.201 80]

W: Failed to fetch http://archive.ubuntu.com/ubuntu/dists/oneiric/Release.gpg  Unable to connect to archive.ubuntu.com:http: [IP: 91.189.92.201 80]

In /etc/resolv.conf remove the existing name servers and add 8.8.8.8 as the primary DNS. This is one of the two DNS servers Google is offering for public use (other 8.8.4.4).

nameserver 8.8.8.8