NetBSD OS PMC wrote:
> 
> The default value of ip6_v6only (sysctl net.inet6.ip6.v6only) has
> been changed.  The new value brings us closer in line with current
> RFC-defined behavior and practices.
> 
> Itojun still has significant concerns about the new default behavior.
> His concerns have been well-documented in
> ftp://ftp.itojun.org/pub/paper/draft-cmetz-v6ops-v4mapped-api-harmful-00.txt
> 
> Best Regards,
> NetBSD OS PMC (core)

The draft is well founded.  I strongly opposed the translation/mapping 
of IPv4 into IPv6 a decade ago.  There was a whole working group 
devoted to the project, and AFAIK, the WG failed interoperability and 
was disbanded. 

The stack should use IPv4 or IPv6 on a per host basis, as indicated by 
its DNS *and* the availability of IPv6 infrastructure, but not both 
concurrently (for a host).  Of course, there could be IPv4 and IPv6 
concurrently (dual stack approach).

Craig Metz is a sharp fellow, and has been working on IPv6 
implementation since the beginning.  We all respect itojun (of course). 

RFCs are not gospel.  RFC-2133/2553/3493 has evolved over time, and is 
"Informational".  The new IPV6_V6ONLY is only in the most recent 
version, and the default value of "off" is manifestly wrong.  

Please leave the default value as "on", as recommended by 
v4mapped-api-harmful.
-- 
William Allen Simpson
    Key fingerprint =  17 40 5E 67 15 6F 31 26  DD 0D B9 9B 6A 15 2C 32