Multiple PTRs for the same IP

Peter Dambier peter at
Fri Jan 26 20:32:47 UTC 2007


the resolver lib has the ability to return more than one ip for every hostname
and more than one hostname for every ip

$> natnum mail.5wc


It works perfectly with /etc/hosts as seen above.

$> natnum


it does work with dns only from hostname to multiple ip-addresses. But with
multiple ptr records it might also work the other way.

Rarely have I seen people doing it and sorry - my resolver lib does not
support it. I think it is a bug in the resolver lib.

Kind regards
Peter and Karin

Fr34k wrote:
> Hello All,
> I'm trying to find something "official" that states, or explains, why multiple
> PTRs for the same IP are not a very good idea.
> Let me explain what I am talking about, and where I am hoping to go with it.
> In previous discussions on this topic, folks have mentioned things like:
>  - most utilities will only use the first PTR returned in a query. So, why have
> many?
>  - many PTRs may require TCP, rather than UDP, query traffic. This may cause
> issues if UDP is expected/enforced (or why initiate unnecessary overhead)
>  - many PTRs may cause confusion when doing an rDNS check on a hostname (eg.
> they may not necessarily match in a round-robin scenario with multiple PTRs --
> counter productive?)
> My google searches find similar blogs that agree that multiple PTRs are a bad
> idea.
> One blog even says it is a "violation" to do so, but without reference to
> back this claim.
> Another tool says that while more than one PTR record for an IP is "legal", but
> it suggests to use only on PTR record for reasons pointed out above.
> While all of the above is excellent feedback from DNS gurus, I have been unable
> to find anything "official" to refer an upper management audience to on this
> topic.
> Does anyone know of an RFC that discusses this (hopefully, in our favor that
> multiple PTRs for the same IP is not a good thing).
> Some other similar reputable source, perhaps, I can reference?
> TIA -- Chris
> PS
> I hope not to offend anyone for the feedback on this topic thus far.
> That is not my intent.
> I am looking for something to support policy. We all know that game, right?
> I hope that is understood.

Peter and Karin Dambier
Cesidian Root - Radice Cesidiana
Rimbacher-Strasse 16
D-69509 Moerlenbach-Bonsweiher
+49(6209)795-816 (Telekom)
+49(6252)750-308 (VoIP:
mail: peter at
mail: peter at

More information about the bind-users mailing list