Summary

Bad guys can abuse some of transition techniques

Don't run 6to4/auto tunnel relay, if you don't need one
Be careful about v4 mapped address

What to do next?
Incorporate checks presented here as much as possible, into original proposals
Publish it as separate document, like "suggestion to implementers" (informational?)
Let us check other proposals as well

Let us deploy native IPv6 network sooner, so that we no longer need tunnels

http://playground.iijlab.net/i-d/draft-itojun-ipv6-transition-abuse-00a.txt