Safari on IPv6 ?

Shane Kerr shane at
Tue Feb 2 13:57:55 CET 2010


On 2010-02-01 11:21, Marco Hogewoning wrote:
> This should be easy, however I can't seem to find the answer online as most articles are about turning off IPv6 instead of one. I noticed Apple's Safari 4.04 defaults to IPv4 instead of IPv6 when both A and AAAA are present. Now you can discuss wether this is a safe default or not, I would really like to know where the little button is to switch this behavior to AAAA first, which I recall used to be the case on earlier editions.

You may be experiencing the effects of Apple's strategy for IPv4/IPv6
dual adoption. You can see a short (9 minute) talk from Stuart Cheshire
at IETF 72 here:

The interesting bit for this discussion starts around minute 02:00 or so.

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.

It's a reasonable solution, I think.

Assuming this is the reason, then the answer is to make your IPv6
connection faster. :)


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