[dns-operations] AXFR support for custom DNS features (Was: Recommended zone serial number format for over 100 changes / day)

Andrew Sullivan ajs at anvilwalrusden.com
Sat Apr 2 20:37:22 UTC 2016

On Sat, Apr 02, 2016 at 10:28:25AM -0700, Robert wrote:
> That's the crux of my confusion.  I've read numerous posts on this
> mailing list and others where people want AXFR support from commercial
> DNS providers that support features which aren't supported by AXR -
> with the consensus being those unsupported records must be dropped.

I think you're conflating "unsupported features" and "unsupported

If a provider encodes its special sauce in RRs in the zone, then
there's no reason to drop the records in AXFR.  There _might_ be
reason, from the provider's point of view, to block the records going
out because of commercial feelings about exposing their tricks and so
on.  Moreover, there's a different problem, in that the receiving
server wouldn't exhibit the behaviour in question anyway, because the
server wouldn't know how to do the special processing: these are
non-standard behaviours.

> It doesn't sound like a usable feature if only parts of a zone are
> transferred.

If you're using non-standard behaviours, you can't expect standard
interoperability.  The whole point of the standard is the

> For those who want AXFR out from a commercial DNS provider, why do you
> want it if it isn't expected to work?

Many commercial DNS providers do bog-standard DNS too.  If you put
only standard RRs in your Dyn-operated zones, you'll get fast anycast
DNS in lots of places.  I am aware that some customers actually do
this with us and other providers at the same time, in order to provide
a multi-vendor kind of resilence.

Best regards,


Andrew Sullivan
ajs at anvilwalrusden.com

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