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

[Name withheld by request]

In article <ec0465$188h$1 at sf1.isc.org> you write:
>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

OK/thanks.  I looked at my O'Reilly "DNS and BIND" book and they show an example
that agrees w/you.  Their extra "A" record is intended for troubleshooting/debugging,
so I expect in general you want to stick w/1 A record per IP address if possible.

> , 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.

Again, the O'Reilly text agrees with you.  Thanks much.

My sense is that, the best way to determine what the cannonical name
for a host is, is to assume that the name pointed to by the PTR 
record is the cannonical name.

>
>                                                                         
>                                           - Kevin