This post addresses network engineers as well as simple users and is trying to popularize and communicate that 6to4 is considered for good reason a harmful mechanism for the global proliferation of IPv6.
On top of various measurements, the experience accumulated during last years has clearly shown that the transition mechanism – once made to easy the migration to IPv6 are no longer capable of aiding us but rather pushing us back.
IETF has been very active in debating over pulling the plug on 6to4. As of the time of this post the following 2 fine examples of this effort are in place. The draft-ietf-v6ops-6to4-to-historic-00 is the one that requires stopping all following development and implementations of 6to4. This is necessary to make sure OS and equipment vendors have 6to4 shut down by default. It has also an impact on some existing equipment certifications that have 6to4 a part of them as well.
We obviously can’t expect 6to4 to disappear overnight and here is draft-ietf-v6ops-6to4-advisory-00 that should serve as a good note on how to properly support existing 6to4 infrastructure to allow 6to4 to fade slowly without affecting user experience.
Here is a very useful link from getipv6.info. It describes the current customer problems that can generally occur with IPv6 and has some wording on 6to4 as well.
All in all, 6to4 is still a useful tool in some knowledgeable hands to make first steps into the IPv6 world. However the reality of IPv4 address exhaustion pushes content and service providers to take decisive steps. With CGNs things will get even worse.
If you are a simple user, an enterprise or a NOC and are looking for an easy way to disable 6to4 on Windows, here is a link to a patch from Microsoft that will heal the 6to4 troubles for you.