[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
Fri Apr 1 17:26:26 UTC 2016

On Fri, Apr 01, 2016 at 10:13:08AM -0700, Robert wrote:
> So then the preference would be dropped?

Anything that _isn't_ an RR would be dropped, yes.  So, …

> how people would find that useful.  For example, most DNS providers
> have some notion of weighted round robin records.

This is quite often not a RR, but some sort of internal trickiness.
Many providers implement this differently to one another.  If the
different providers shared a common format for how to express this,
then it'd be preserved; otherwise, it likely wouldn't.  For instance,
I know that our implementation of this sort of thing at Dyn (my
employer) in fact uses a special RR.  It will normally survive zone
transfers through unpatched servers (we've done it); but usually when
we do outbound zone transfers these things are filtered out because
the other name server doesn't do what we do with this data (so it'd be

> Please forgive my ignorance, I don't use AXFR and I'm just trying to
> educate myself on how people would expect this to work because I often
> hear people wanting this feature from various commercial DNS
> providers, most of whom support features which are not supported by

It's not necessarily strictly that the features aren't supported by
AXFR.  It's that there's no well-known way to configure these
behaviours across provider -- basically, they're not part of the
standard, so they don't interoperate.

Best regards,


Andrew Sullivan
ajs at anvilwalrusden.com

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