Multiple PTRs for the same IP

[Peter Dambier]

Hello,

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

host_look("212.97.45.53","a-root.maxmv.org","3563138357").
host_name("212.97.45.53","a-root.maxmv.org").
host_alias("mx3.memor.net","a-root.maxmv.org").
host_alias("mr1.mastrocinque.net","a-root.maxmv.org").
host_alias("mail.ttf","a-root.maxmv.org").
host_alias("mail.5wc","a-root.maxmv.org").
host_alias("mail.publicroot.org","a-root.maxmv.org").

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

$> natnum www.interpixel.de

host_look("81.88.40.52","www.interpixel.de","1364731956").
host_name("81.88.40.52","proxy2.kontent.com").
host_look("81.88.40.51","www.interpixel.de","1364731955").
host_name("81.88.40.51","proxy1.kontent.com").

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: sipgate.de)
mail: peter at peter-dambier.de
mail: peter at echnaton.serveftp.com
http://iason.site.voila.fr/
https://sourceforge.net/projects/iason/
http://www.cesidianroot.com/