Nah, the service provider tells the client what to use via SRV records.
In most cases the service provider is going to know if IPv4 or IPv6 is going
to work better. They use different DNS names for the v4 and v6 interfaces
and prioritize them accordingly.
In most cases though the server is going to be IPv4 only or have equally
good IPv4 and IPv6.
On the client end the client is going to have a consistently better
experience with v4 or v6. And that information can be used to inform the
choice when making future connections.
The only case where I can see a client preferring IPv6 over 4 is when they
are behind a super-NAT and the v4 service is degraded. Or when they are
attempting to accept an incoming connection for VOIP or video conferencing.
The key is to take the decision out of the hands of the application software
so that it can be taken by the platform and allow the experience from one
connection to be used to inform the choice made on the next.
On Thu, Jun 24, 2010 at 7:57 PM, David Conrad <drc(_at_)virtualized(_dot_)org>
wrote:
On Jun 24, 2010, at 4:48 PM, Mark Andrews wrote:
The third choice is to do a non-blocking connect to IPv6 then if that
does
not succeed in 1 or 2 seconds (most successful connects are within this
peroid but connect failures are considerably longer) initiate a non
blocking
IPv4 connection and keep whichever completes first and abort the other.
That sounds like a variation of the v6-then-v4 serial case, just slightly
accelerated. But maybe I'm missing something...
Regards,
-drc
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