Re: Newbie: in-addr.arpa file for a C Class

Most likely I'm confusing what the customer is looking for to be
honest.
Heres my confusion. In our DNS server for block 216.X.X we have this
file:

X.X.216.in-addr.arpa. 86400 SOA ns1.myserver.net
support.myserver.net (
2003012918 ; serial
3600 ;refresh
600 ;retry
604800 ;expire
86400 ) ;minim
;
; Nameservers
;
NS ns1.myserver.net.
NS ns2.myserver.net.
;
; Other records for this domain (as domain.com).
;
; example
; IN A cus.tom.er.ip
; MX 0 mailserver.domain.com
;
; Host Records (xxx.domain.com)
;
localhost IN A 127.0.0.1
;
; Momentum Securities Reverse Entries
;
10 IN PTR mail.domain1.com.
11 IN PTR mail.domain2.com.
12 IN PTR mail.domain3.com.
112 IN PTR machine1.domain4.com.
135 IN PTR bigblue.domain5.org.

So obviously if I lookup .10 in this block, I get the associated
domain. The odd thing is, when I look up an IP that does not have a
PTR record I get:


Name: wsip-216-X-X-9.sub.mydomain.net
Address: 216.231.10.9

How is that done??
Thanks again for the help and education.