[dns-operations] Multiple A/AAAA RRs associated with an NS RR

John Kristoff jtk at cymru.com
Fri May 3 22:15:28 UTC 2013

Most authoritative servers, and presumably most operators, associate a
single A, AAAA or pair of those two to a single NS RR, but I have seen
cases where this is not true.

For instance, representative of the more common configuration,
example.org has an NS RR of b.iana-servers.net and that name in turn has
one A and one AAAA associated with it.

However, imagine b.iana-servers.net actually maps to multiple A RRs.

I've seen cases where PTRs can get out of whack.

I could imagine server selection or round robin algorithms giving
somewhat unpredictable and potentially suboptimal results.

Perhaps even some issues with an suboptimal set of additional records
being returned.

On the other hand... if the NS names are in different zones, perhaps
this adds some reliability.

I'm curious if anyone is aware of, or can envision, any actual problems
or real benefits with this A/AAAA overloading, for a lack of a better
term since I'm not sure what to call it.

Thanks to my friend Ed Lewis who entertained a version of this question
some time back off-list and began his response in his characteristically
delightful way with "Problems get solved more easily when it's a genius
and an idiot working together".


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