Safari on IPv6 ?

Martin Millnert martin at
Tue Feb 2 14:13:16 CET 2010

On Tue, 2010-02-02 at 13:57 +0100, Shane Kerr wrote:
> As I understand it, Safari does the equivalent of:
> 1. DNS lookup
> 2. TCP connection
> 3. HTTP request
> In both IPv4 and IPv6 at the same time. Whichever gets to step #3
> first goes to completion "wins", and the other is canceled.
> Note that once the A and AAAA record are in the DNS cache, then you
> are really just looking at connecting on whichever TCP session opens
> first. 


this might very well be their goal, but it doesn't seem to be what's
going on, since Ron showed us on Monday that the mDNSResponder just
shuts down the remaining queries (one lingering AAAA in the example),
after having received its first reply.

In other words, the actual implementation, intended or not, is right now
that whoever accomplishes #1 first, may continue.

I would be more inclined to agree with that whoever performs #3 first
wins, than #1.  DNS lookup speed says nothing definite about IPv4 vs
IPv6 network/routing topologies and round trip times.

Martin Millnert <martin at>
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