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

Doug Barton dougb at dougbarton.us
Fri May 3 22:34:39 UTC 2013

It's very common, and does not present any problems in operational 
practice. For example, from the root zone:

Number of IPv4 hosts:		1209
Number of IPv4 addresses:	1157

Number of IPv6 hosts:		 551
Number of IPv6 addresses:	 520

Situations where there are more addresses than hosts are not uncommon 
either, and often result from either a transition in progress, or a 
misunderstanding of what "multiple NS records" means.



On 05/03/2013 03:15 PM, John Kristoff wrote:
> 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".
> John

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