DNS Sample Reverse MAP Zone File

This file (192.168.0.rev) is the sample reverse map zone file used throughout this Chapter and has the following characteristics.

1. Two name servers are used one internal (ns1) and one external (ns2) to the domain
2. The mail service is external to the domain (provided by a third party)
3. FTP and WWW services are provided by the same host
4. There are two hosts named bill and fred
5. The host addresses are all in the class C private address range 192.168.0.0 (a slightly artificial case)

The Resource Records are all defined separately.

$TTL	86400 ; 24 hours could have been written as 24h or 1d
$ORIGIN 0.168.192.IN-ADDR.ARPA.
@  1D  IN	 SOA ns1.example.com.	mymail.example.com. (
			      2002022401 ; serial
			      3H ; refresh
			      15 ; retry
			      1w ; expire
			      3h ; minimum
			     )
; server host definitions
1      IN  PTR    ns1.example.com.
2      IN  PTR    www.example.com.            
; non server domain hosts
3      IN  PTR    bill.example.com.  
4      IN  PTR    fred.example.com.   

Hosts defined with CNAME Resource Records do not have PTR records associated. This is not any form of BIND rule. A IP address can only be defined once with a PTR RR. It could be either the A record or the CNAME record - we just happened to choose the A RR.