If you define two A Records with the same IP address then when you come to define the Reverse Mapping (look-up) file you can only map a single name to the IP address. Increasingly mail systems as part of an anti-spam strategy and others may perform a dual look-up, IP to name then name to IP. A Reverse Mapping query will only return the right result for joe in the example below not for www. In this simple case use of a CNAME record for www could fix the problem.
; zone file fragment joe IN A 192.168.254.3 ; joe & www = same ip www IN A 192.168.254.3 ; reverse in-arpa file fragment .3 IN PTR joe.example.com.
If you define multiple A Records for load balancing or round robin strategy the same problem arises. In a dual look-up, IP to name then name to IP, system this will only work for mail in the example below not for any others.
; zone file fragment mail IN A 192.168.254.3 ; round robin IN A 192.168.254.4 IN A 192.168.254.5 ; reverse in-addr.arpa file fragment .3 IN PTR mail.example.com. .4 IN PTR mail1.example.com. .5 IN PTR mail2.example.com.
3 reverse map
4 dns types
5 install bind
8 dns records
12 bind api's
13 dns security
bits & bytes
notes & tips