[AusNOG] IPv6: Who's dual stacked? Why don't I look stacked?
marka at isc.org
Fri Mar 8 11:44:13 EST 2013
In message <214A7506-A76B-4C69-8ADD-B563217C995F at apnic.net>, Geoff Huston writes:
> On 08/03/2013, at 10:10 AM, Mark Andrews <marka at isc.org> wrote:
> >> For that matter, really of what apps do and do not
> >> support IPv6 transit and which do not, and even if an app (a mail
> >> for example) supports IPv6, whether the server (Internode's mail
> server for
> >> example) supports IPv6. And finally, if everything supports IPv6, what
> >> priority is given to IPv6 over IPv4 (or vice versa).
> > IPv6 is given priority over IPv4 for most things.
> Thats not always the case any more.
Hence "for most things".
> Various implementations of "happy eyeballs" out there today use
> algorithms that have different embedded heuristics as to which protocol
> to select when given a choice.
And they still do a bad job compared to the simple if you don't get
a connect in 200ms start a parallel connection. Safari sucks badly
on Mountain Lion when there a little delay with DNS responses like
there is when you are talking to the ORG servers to get DNSKEY
behind a tunneled connection over IPv6. Some of them force the
client to TCP then you have to hope the PMTUD kicks in. Just set
USE_MIN_MTU on the socket and let the UDP packets be fragmnented
rather then force TCP and if you are going to force TCP set USE_MIN_MTU
on the TCP socket as well so that PMTD can be avoided or set the
interface MTU to 1280.
> The old algorithm of "Try V6 and wait for the TCP connection to fail, and
> if it does then try V4" imposed either slow (20s, Windows), tediously
> slow (75s, FreeBSD) or catastrophically slow (108s, Linux) delays when
> the IPv6 connection was unable to complete. These days many browser/OS
> combinations do the dual protocol dance in parallel and end up using the
> fastest protocol rather than always just preferring to initiate a
> connection on IPv6 whenever possible.
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742 INTERNET: marka at isc.org
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