[virt-tools-list] Installing Ubuntu 12 on Centos 6 Host not using ISO

[Dennis Jacobfeuerborn]

Hi,
I'm trying to find out how to install an Ubuntu guest on a Centos 6 Host
without using an ISO but I cannot find the proper URL to use.
I usually only use Centos guest and one URL from a mirror would be
"http://ftp.halifax.rwth-aachen.de/centos/6.3/os/x86_64" but I can't find
the corresponding Ubuntu version of such an URL on Google.
Any ideas?

Regards,
  Dennis