Hey,

On 6 Jul 2019, at 19:59, Witold Krecicki <w...@isc.org> wrote:

> But why put it out-of-band when it can be in-band?

I don't think there's a good general answer to this. Sometimes in-band 
signalling is good; other times out-of-band signalling has proved to be safer. 
I'm talking very generally, here, not directly about your proposal.

As far as this particular idea goes, I mentioned before what had given me 
pause: we're talking about taking a protocol where every RRSet in a zone to 
date has been public and is made available in DNS responses. Any server that 
doesn't implement this new mechanism would presumably treat the new covert 
RRTypes as they would any other unknown/opaque type and make the data public.

There is hence an operational risk that data will leak (e.g. by configuration 
changes, software downgrades that are pragmatic necessities, side systems that 
publish zone data in ways other than the DNS).

By keeping data that is already exchanged over a (manual) out-of-band channel 
separate, and not packaging them up with zone data, the existing segregation of 
private vs. public is preserved and the task is simply to automate a process 
that is currently manual.

This might sound like a very high-level concern, but I suspect there are 
ramifications of changing the security model of the data published in a zone 
that extend beyond the operation to the wider architecture, e.g. what to do 
with PII that is published in a covert record, and what extra work results from 
the changed risk profile of that data? In a segmented security architecture, 
what are the implications of sensitive material being mixed with public 
information?


Joe

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