Yahoo and IPv6

Iljitsch van Beijnum iljitsch at
Wed May 11 08:53:00 UTC 2011

On 11 mei 2011, at 2:39, Karl Auer wrote:

> On Wed, 2011-05-11 at 10:19 +1000, Mark Andrews wrote:
>> For the record Apple's current iChat (the OS (10.6.7) is completely
>> up to date) fails such a test.  It will try IPv6 and not fallback
>> to IPv4.  End users shouldn't be seeing these sorts of errors.

Hm, I've had a very hard time finding any IPv6-capable servers to let my iChat talk to...

> Is that possibly a failure of the underlying resolver library? Do other
> applications on the same platform behave correctly?

Apple's Mail application used to do this, but after many years they fixed this, it will now fall back to IPv4 without trouble. This isn't a resolver issue, as the resolver can't know whether IPv6 connectivity does or doesn't work. The resolver simply gives applications that don't explicitly ask for a particular address type all of the addresses of all types for which the system currently has connectivity, I think as determined by the presence of a default route, maybe the presence of an address also matters.

What applications need to do when they connect to a remote server is to try the next address when the first one fails and cycle through all addresses before giving up. Of course with IPv4 having multiple addresses is extremely rare so IPv4 applications typically don't bother with this, so it has to be addressed when IPv6ifying applications.

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