Mac OS X IPv6 behaviour update

Tore Anderson tore.anderson at
Tue Sep 21 11:29:57 CEST 2010

* Bernhard Schmidt

> Do you know whether the resolver has been fixed, too (MacOS X 10.6
> querying both AAAA/A at the same time, but only accepting the first
> answer -> broken failover and non-deterministic AFI selection)?


from what I can tell, there appears to be a timeout of approx. 125ms
before the resolver stops waiting for AAAA responses.  In other words,
if the AAAA response is received > ~125ms later than the A response (or
this could possibly be 125ms since the AAAA query was transmitted), IPv4
connectivity is used even though IPv6 would normally be preferred.

It is much more insistent on getting A responses, though.  If it doesn't
receive a response quickly, it retransmits the query several times.  It
didn't start preferring 6to4 to IPv4 until I delayed the A responses
more than 25 seconds.

I don't know if these timeouts have changed since OS X 10.6.4, though.

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

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