DNS loopback zone

The loopback zone is part of a DNS configuration.
Its purpose is to handle the 127.0.0.0/24 network.
By convention and good practice each DNS server must handle it.
Naturally, the above recommendation doesn't apply to DNS root servers. 
In general the localhost number is 127.0.0.1.
Hence, the zone file is called db.127.0.0.

Consider the example given on the post DNS internal root.
The top-level (below DNS internal roots) internal DNS servers are:

• NS00.business.corp
• NS01.business.corp 
• NS02.business.corp 

  
Each of them would have the following loopback zone configuration:
(the following are the contents of db.127.0.0)

;  
;       Business Corp.  
;  
;       The loopback zone.
;       last update:    July 31, 2014.  
;

$TTL 3h

@  IN  SOA  NS00.business.corp.  hostmaster.business.corp.  (
            1    ; Serial
            3h   ; Refresh after 3 hours
            1h   ; Retry after 1 hour
            1w   ; Expire after 1 week
            1h ) ; Negative caching TTL of 1 hour

; Authoritative name servers.
 
   IN  NS  NS00.business.corp.
   IN  NS  NS01.business.corp.
   IN  NS  NS02.business.corp.

; The localhost PTR record.
 
1  IN PTR localhost.

; End of File.
 
In this particular case /etc/named.conf must contain:

zone "0.0.127.in-addr.arpa." in {
  type master;
  file "db.127.0.0";
  notify no;
};