[ntp:questions] http://www.ntp.org/ => a blank page?

Danny Mayer mayer at ntp.org
Mon Mar 9 03:47:09 UTC 2009

Dave Hart wrote:
> On Mar 5, 10:14, Martin Burnicki <martin.burni... at meinberg.de> wrote:
>> The IPv4 address is used only after the IPv6 address has timed out, even
>> though (as far as I understand it) the DNS server first returns an IPv4
>> address, then an IPv6 address:
>> # host support.ntp.org
>> support.ntp.org has address
>> support.ntp.org has IPv6 address 2001:4f8:0:2::23
> That's a bit misleading.  At the protocol level the queries are often
> distinct, asking for A or AAAA records.  type=any will return both but
> is not typically used in apps.  At the app level, if the app looks up
> a name indicating both IPv4 and IPv6 addresses are desired, platform
> and site policies come into play

getaddrinfo() which is used by all newer apps returns both IPv4 and IPv6
unless you specify a particular type. It has nothing to do with site
policy and they do not come into play. The query is controlled solely by
the app. The app may have additional controls on whether or not it wants
to query for IPv4, IPv6 or both.

>> I know a possible solution would be to use a IPv6-over-IPv4 tunnel to the
>> internet. However, if this has not been set up then access may fail for a
>> reason which is not obvious.
>> AFAIK some browsers, e.g. Firefox, can be configured to prefer either IPv4
>> or IPv6, so this can be solved without a tunnel.
> It sounds like you use a disconnected IPv6 network alongside a
> connected RFC1918 v4 network internally.  I wonder if you could get by
> using only link-local addresses for your internal IPv6 network?  I
> believe that would solve the problem because your stack would know it
> can't connect to a global v6 address from a machine with only link-
> local v6 addresses.

The stack has no knowledge of whether it can connect to a global IPv6
address. Only the routers will be able to do that.

>> A good solution would be to let the local DNS server discard IPv6 addresses
>> returned from forwarders while maintaining IPv6 suuport for the local
>> zone/network, but I currently don't know if/how this can be configured for
>> bind 9.
> This may indeed be the best option for your configuration.  I wouldn't
> call it a good solution, though.  Your machines should be able to
> handle seeing AAAA records via IPv4-accessible DNS even if they can't
> use them.  I'd dig into configuring the machines to use IPv6 as a last
> resort before considering DNS server-based AAAA filtering.

It cannot be done by the DNS.

> Cheers,
> Dave Hart
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