>>Oh, and: are there any implementations already existing under a BSD 
>>license, e.g. from KAME, FreeBSD, OpenBSD or DragonflyBSD that may be 
>>used?
> 
> 
> Under BSD license, there is a Netgraph implementation for FreeBSD,
> ng_teredo.  That code may be a good starting point.  I strongly prefer
> that Teredo for NetBSD does not depend on Netgraph.
> 
> I also strongly prefer that the tunneling encapsulation/decapsulation
> occurs in the kernel, instead of in a userland process (e.g., GPL-licensed
> Miredo), for performance reasons.  I am open to demonstrations that the
> overhead of a userland implementation is negligible.
> 

Right, the kernel space is the place to put the Teredo code.
I never understood why NetBSD people do not port Netgraph on their OS, 
it is simple to port ! and it is a powerfull tool box.

For you information, we did not implement the client part of teredo into 
ng_teredo because we do not need it. We only use the relay and server 
part. However, if somebody wants to support extend it, they can send me 
the patch against ng_teredo and I'll commit it.

Regards,
   Vincent