The main showstopper for IPv6 in my private network environment was the non-availability of IPv6 payload support on OpenVPN's multi-client server mode. I am using the OpenVPN multi-client server mode exensively with a number of clients, and adding IPv6 to my OpenVPN network would have meant re-building most of it without multi-client server mode. This would mean having a rather dirty construction with one process per client or even **gasp** bridging. I did not have the heart to actually do this and stayed with IPv4.
Thankfully, these times are over: Gert Döring, Thomas Glanzmann, Bernhard Schmidt and Jan Dirnberger spent the better part of the christmas holidays implementing IPv6 payload support in OpenVPN multi-client server mode. They have published a patch against OpenVPN 2.1 and a number of binary packages implementing this feature that I've been waiting for.
Unfortunately, the IPv6-over-OpenVPN-multi-client-mode patch clashes with the well-known OpenVPN-over-IPv6 patch, so I had to disable it in my locally patched version of Debian's OpenVPN package. Bernhard's binary packages contain both patches.
Enabling IPv6 multi-client server mode is really a breeze. Add server-ipv6 and route-ipv6 statements to your server configuration, and you're done. Client-config-dir works for IPv6 as well, so I can assign static IPv6 addresses to the clients and tell them to point their IPv6 default route into the tunnel from the server by virtue of a ifconfig-ipv6-push and a push route-ipv6 statement inside the client-config-dir file.
That's it. Clients with unpatched client software can still connect (and will only get IPv4, just as before), and clients with patched client software will transparently get IPv6 additionally to the IPv4 tunnel. Now, I only have to pay attention again what services are running on my laptop - it's publicly visible on the intarwebs again.
Guys, your work rocks. I really really appreciate that. Good Job. I owe you more than a beer. Now we only need to convince OpenVPN upstream to accept your patch.