Comment 1 for bug 392828

Assuming you don't have IPv6 networking yet, here is a short instruction on how to get connected.

Use a tunnel broker like SixXS to acquire an IPv6 tunnel, or maybe your provider can actually hook you up with IPv6 (I'm told the dutch provider XS4All actually offers that, mine doesn't). To get started with SixXS, see http://www.sixxs.net/faq/account/?faq=10steps for 10 easy steps to IPv6.

Once you have your tunnel set up, you need to apply for an IPv6 network range, as you need a separate machine to test IPv6 only networking if you run a tunnel. SixXS provides documentation on how to set up the network range.
A virtual machine in KVM works just fine, that's what I'm using myself, I have not tried with VirtualBox and VMware can't do IPv6 for all I know. Once your IPv6 only machine is set up and can e.g. ping6 ipv6.google.com, just turn off the ipv4 addresses. Verify that you don't have an IPv4 route to the internet anymore. Now try to apt-get update and you will find that security.ubuntu.com is unreachable.