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IPv6 status in OS X 10.6.5
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IPv6 status in OS X 10.6.5


the 6to4/IPv4 preference problem I've posted about a few times earlier
appears to be solved in the OS X 10.6.5 previews.  I'd like to send a
big «thank you» to everyone in Apple involved in making that happen!

However, there's still some rough edges and in sending this message I'm
hoping there's a chance they too will get included in the final release
of 10.6.5.

First, the Teredo prefix (2001:0::/32) is still preferred above IPv6.
Teredo provides inferior, last-resort type connectivity (much like
6to4), so it should be de-preferred in the same way as 6to4 is.

Second, if OS X has a default route but no globally scoped IPv6 address
(e.g. after receving a RA with no prefix information), Firefox seems to
break towards dual-stack sites.  Using tcpdump I can see that only
Firefox solicits AAAA records in this situation, while Safari and Chrome
appears to optimise them away - perhaps by supplying ai_family=AF_INET
when calling getaddrinfo().  This problem has been been observed in the
wild by Heise who recently went dual-stack, see:
This situation also broke Safari in OS X 10.6.4, while Chrome handled
in well in both 10.6.4 and 10.6.5.

I also did some brief testing on the bug about OS X ignoring AAAA
responses if they arrive later than the A responses.  From what I can
tell, there's a timeout of about 125ms before OS X gives up waiting for
AAAA responses.  So if a user's DNS resolver has only the A record
cached, OS X might end up preferring IPv4 in situations where IPv6 would
normally be preferred.  The opposite is not true, however.  OS X 10.6.5
did not start to prefer IPv6 in situations where IPv4 would normally be
preferred (e.g. when using 6to4) before I delayed the A responses by 25
seconds.  I do not know if this behaviour is the exact same as in 10.6.4
or not, though.

Best regards,
Tore Anderson
Redpill Linpro AS -
Tel: +47 21 54 41 27
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