[ntp:questions] What to do about broken IPv6 sites

Danny Mayer mayer at ntp.org
Thu Jun 25 03:57:14 UTC 2009

Rob wrote:
> Rick Jones <rick.jones2 at hp.com> wrote:
>> Allen Kistler <ackistler at oohay.moc> wrote:
>>> For example, http://www.ntp.org.
>>> NTP.org has a perfectly good IPv4 site, but the IPv6 site doesn't
>>> answer to SYNs.  I have no problem with other IPv6 sites, but maybe
>>> I'll find some in the future.
>>> Since RFC-compliant behavior is to try the IPv6 address first, I
>>> have to timeout on every page element before switching to IPv4.
>>> I was wondering what the options are to deal with the situation.  I
>>> don't have control of the ntp.org DNS domain (or any other broken
>>> domains I might find).  Keeping a list in iptables for special
>>> behaviors for specific IPv6 addresses really isn't attractive.
>>> As more sites put up IPv6 versions, I expect there to be a lot of
>>> brokenness that won't be a high priority to fix as long as 99% of
>>> everybody is still on IPv4.  What's the most manageable way to deal
>>> with this?
>> I don't know about the general question, but there are likely folks in
>> comp.protocols.time.ntp who know about the www.ntp.org site and its
>> IPv6 status, so lets redirect the specific issue there. (I've set the
>> Followup-to: header on this post to that end)
> I know that it is not what the RFC says, but I think that when you
> want usable dual-stack behaviour you need to give IPv4 preference
> for now (use IPv6 only when no IPv4 record is available or connection
> fails).

No, that's not true. Too many applications would fail if that happened.
If you want to use IPv6 and the path exists to support access via IPv6
it will work.


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