2 A records, 2 PTR records, just 1 IP - is this proper?

[Kevin Darcy]

Name withheld by request wrote:
> Hi:
>
> Is DNS setup incorrectly for host 10.123.85.254, based in this?:
>
>   $ dig -x 10.123.85.254 +short
>   z7engs005.oursubdomain.ourdomain.com.
>   tapemonkey.oursubdomain.ourdomain.com.
>   $ dig z7engs005.oursubdomain.ourdomain.com a +short
>   10.123.85.254
>   $ dig tapemonkey.oursubdomain.ourdomain.com a +short
>   10.123.85.254
>
> In my limited experience w/DNS I thought that you could have only one
> name returned when you do a "dig -X"; ie PTR records for a given IP point
> to exactly 1 name.
>
> I also thought you could have only one A record associated with a given IP address,
> and that this A record defined the canonical name for the host.
>
>   
No, you can have multiple A RRs pointing to the same address, and a 
single in-addr.arpa name can own multiple PTR RRs (or for that matter, 
records of other types). The latter case (owning multiple PTRs) is 
rather pointless, though, since very few clients, if any, look beyond 
the first PTR in the list.

                                                                         
                                           - Kevin