IPv6 Source Address Selection on Mac OS X Lion

Bjoern A. Zeeb bzeeb-lists at lists.zabbadoz.net
Sat Dec 17 02:50:59 CET 2011

On 16. Dec 2011, at 18:13 , Gert Doering wrote:

> Hi,
> On Fri, Dec 16, 2011 at 06:11:11PM +0000, Mark Blackman wrote:
>>> On Thu, Dec 15, 2011 at 09:31:42AM -0800, Dan Wing wrote:
>>>> It depends on your definition of "better".  If your definition is
>>>> "prefer IPv6", you are right that OSX Lion's algorithm fails.  If
>>>> your definition is "connect to whichever is fastest", OSX Lion's
>>>> algorithm wins.
>>> "consistent behaviour".  And this is where Lion fails, because it
>>> flip-flops back and forth between protocols even if nothing changes
>>> in the network.

You want consistent behaviour?  Do what I do.

>> Isn't this behaviour what Chrome does too?
>> http://src.chromium.org/viewvc/chrome?view=rev&revision=85934
> on a network where IPv4 and IPv6 have the same (or close) RTTs, chrome
> will *consistently* pick IPv6.  Not "sometimes IPv6, sometimes IPv4".
> Big difference.
> The general idea of HE is good.  HE-in-Lion a step backward.

The missing knob to turn it off sucks badly in either however and while I stop
caring myself I am seeing the problem you describe in dual-stacked networks for
others unfortunately and would love to have a switch to flip to get v6 first v4
then back (at least on demand).

Here, there is no IPv4 address anymore usually, a 127.1 on Lion.
The v4 link-local on XP doesn't seem to matter much currently for IE luckily
and on FreeBSD/PC-BSD the no-IPv4 stack does the job as well:)  No decisions to
make for complex algorithms.  Deterministic behaviour.  User really happy.
Debugging is simpler.  Problem solved.  Good night.


Bjoern A. Zeeb                                 You have to have visions!
   It does not matter how good you are. It matters what good you do!

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