Reverse zone and PTR record

After configure master record now here we are Create Reverse zone file for convert ip Address to name. For hosting PTR record in DNS we need to create Reverse zone file entry in /etc/named.conf file. same like below
    zone "0.168.192.in-addr.arpa" IN {
              type master;
              file "192.168.0.zone";
    };

Edit reverse zone entry in /etc/named.conf
[root@master ~]# vim /etc/named.conf
[root@master ~]# cat /etc/named.conf
//
// named.conf
//
// Provided by Red Hat bind package to configure the ISC BIND named(8) DNS
// server as a caching only nameserver (as a localhost DNS resolver only).
//
// See /usr/share/doc/bind*/sample/ for example named configuration files.
//
// See the BIND Administrator's Reference Manual (ARM) for details about the
// configuration located in /usr/share/doc/bind-{version}/Bv9ARM.html

options {
        listen-on port 53 { 127.0.0.1; 192.168.10.2; };
        listen-on-v6 port 53 { ::1; };
        directory       "/var/named";
        dump-file       "/var/named/data/cache_dump.db";
        statistics-file "/var/named/data/named_stats.txt";
        memstatistics-file "/var/named/data/named_mem_stats.txt";
        allow-query     { localhost; 192.168.10.0/24; };

        /*
         - If you are building an AUTHORITATIVE DNS server, do NOT enable recursion.
         - If you are building a RECURSIVE (caching) DNS server, you need to enable
           recursion.
         - If your recursive DNS server has a public IP address, you MUST enable access
           control to limit queries to your legitimate users. Failing to do so will
           cause your server to become part of large scale DNS amplification
           attacks. Implementing BCP38 within your network would greatly
           reduce such attack surface
        */
        recursion yes;

//      dnssec-enable yes;
//      dnssec-validation yes;

        /* Path to ISC DLV key */
        bindkeys-file "/etc/named.iscdlv.key";

        managed-keys-directory "/var/named/dynamic";

        pid-file "/run/named/named.pid";
        session-keyfile "/run/named/session.key";
};

logging {
        channel default_debug {
                file "data/named.run";
                severity dynamic;
        };
};

zone "." IN {
        type hint;
        file "named.ca";
};

zone "zmailtech.com" IN {
        type master;
        file "zmailtech.com.zone";
};

zone "10.168.192.in-addr.arpa" IN {
        type master;
        file "10.168.192.zone";
};

include "/etc/named.rfc1912.zones";
include "/etc/named.root.key";

[root@master ~]#

PTR records are used for the Reverse DNS (Domain Name System) lookup. Using the IP address you can get the associated domain/hostname. An A record should exist for every PTR record. The usage of a reverse DNS setup for a mail server is a good solution.

Now here we are hosting PTR Record in DNS service.
Create reverse zone file, we are copy named.loopback file into 10.168.192.zone file for revers zone

[root@master ~]# cat /var/named/named.loopback > /var/named/10.168.192.zone

Assigning proper permission and owenership on zmailtech.com.zone file.

[root@master ~]# ls -l /var/named
total 24
-rw-r--r--. 1 root  root   168 Dec 14 16:19 10.168.192.zone
drwxrwx---. 2 named named   49 Dec 14 13:43 data
drwxrwx---. 2 named named   60 Dec 14 16:11 dynamic
-rw-r-----. 1 root  named 2281 May 22  2017 named.ca
-rw-r-----. 1 root  named  152 Dec 15  2009 named.empty
-rw-r-----. 1 root  named  152 Jun 21  2007 named.localhost
-rw-r-----. 1 root  named  168 Dec 15  2009 named.loopback
drwxrwx---. 2 named named    6 Aug  4 13:43 slaves
-rw-r--r--. 1 root  named  470 Dec 14 13:44 zmailtech.com.zone
[root@master ~]#

Change 10.168.192.zone reverse zone file group owner to named group owner

[root@master ~]# chgrp named /var/named/10.168.192.zone
[root@master ~]# ls -l /var/named
total 24
-rw-r--r--. 1 root  named  168 Dec 14 16:19 10.168.192.zone
drwxrwx---. 2 named named   49 Dec 14 13:43 data
drwxrwx---. 2 named named   60 Dec 14 16:11 dynamic
-rw-r-----. 1 root  named 2281 May 22  2017 named.ca
-rw-r-----. 1 root  named  152 Dec 15  2009 named.empty
-rw-r-----. 1 root  named  152 Jun 21  2007 named.localhost
-rw-r-----. 1 root  named  168 Dec 15  2009 named.loopback
drwxrwx---. 2 named named    6 Aug  4 13:43 slaves
-rw-r--r--. 1 root  named  470 Dec 14 13:44 zmailtech.com.zone
[root@master ~]#


Edit PTR record in 10.168.192.zone Revers zone
 
[root@master ~]# vim /var/named/10.168.192.zone
[root@master ~]# cat /var/named/10.168.192.zone
$TTL 1D
@       IN SOA  ns1.zmailtech.com.  admin.zmailtech.com. (
                                        2017121501      ; serial
                                        1D      ; refresh
                                        1H      ; retry
                                        1W      ; expire
                                        3H )    ; minimum

        IN      NS      ns1.zmailtech.com.
        IN      A       192.168.10.2

2       IN      PTR     ns1.zmailtech.com.
2       IN      PTR     mail.zmailtech.com.
[root@master ~]#

Need to restart bind (named) service after change in DNS Records zone file.
[root@master ~]# systemctl restart named

Lets check PTR record with dig -x command.

[root@master ~]# dig -x 192.168.10.2

; <<>> DiG 9.9.4-RedHat-9.9.4-50.el7 <<>> -x 192.168.10.2
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 28756
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 1, ADDITIONAL: 2

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;2.10.168.192.in-addr.arpa.     IN      PTR

;; ANSWER SECTION:
2.10.168.192.in-addr.arpa. 86400 IN     PTR     ns1.zmailtech.com.
2.10.168.192.in-addr.arpa. 86400 IN     PTR     mail.zmailtech.com.

;; AUTHORITY SECTION:
10.168.192.in-addr.arpa. 86400  IN      NS      ns1.zmailtech.com.

;; ADDITIONAL SECTION:
ns1.zmailtech.com.      86400   IN      A       192.168.10.2

;; Query time: 1 msec
;; SERVER: 192.168.10.2#53(192.168.10.2)
;; WHEN: Thu Dec 14 16:10:57 IST 2017
;; MSG SIZE  rcvd: 134

[root@master ~]#