Mac OSX 10.7

[Shane Kerr]

Arturo,

On Thu, 2011-07-21 at 12:53 -0300, Arturo Servin wrote:
> 	What transport is used to query the DNS server, IPv6 or IPv4, i.e. If
> the host has the IPv4 and IPv6 address of the resolver, which one is
> used?

In most other Unix systems the addresses are just used in the order they
appear in /etc/resolv.conf. 

As in many things, Apple doesn't work this way. (In this case that's
good, because the /etc/resolv.conf behavior is crap.) Since 10.6, 
Mac OS X uses mDNSResponder for all DNS lookups, and appears to have an
algorithm that cycles between resolvers based on reachability:

http://support.apple.com/kb/HT4030

One can only hope that IPv4 and IPv6 servers are treated equally, but I
don't know for sure. Maybe someone with a working dual-stack resolver
and Mac OS X 10.7 can do some measurement and let us know?

--
Shane