Yahoo and IPv6

Mark Andrews marka at
Wed May 11 13:07:26 UTC 2011

In message <03C70CDE-8169-437B-8394-26F839413893 at>, Iljitsch van Beijn
um writes:
> 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...

Well I found this bug because the jabber server was IPv4 only and
the box it is on got a AAAA address.  The jabber server is now
running dual stack with the IPv6 ports being forwarded to the IPv4
ports.  It's not optimal but it works.

> > 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.=

This is basic RFC 1123 multihome support.

Also see

Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: marka at

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