Configure CNAME Record

CNAME records are referred to as alias records since they map an alias to its canonical name. CNAME records allow an administrator to point multiple systems to one IP without specifically assigning an A record to each host name. If your server IP ever changes, you only have to change one A record’s IP address to update all associated records.

# Edit below line in /var/named/zmailtech.com.zone file.
 
[root@master ~]# vim /var/named/zmailtech.com.zone
[root@master ~]# cat /var/named/zmailtech.com.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.
ns1     IN      A       192.168.10.2
master  IN      A       192.168.10.2

;CNAME Record
www     IN      CNAME   master.zmailtech.com.
ftp     IN      CNAME   master.zmailtech.com.
smtp    IN      CNAME   master.zmailtech.com.[root@master ~]#

After Edit CNAME Record we need to restart named service.

[root@master ~]# systemctl restart named


Now we test CNAME Record www.zmailtech.com via dig command

[root@master ~]# dig www.zmailtech.com

; <<>> DiG 9.9.4-RedHat-9.9.4-50.el7 <<>> www.zmailtech.com
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 52896
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 1, ADDITIONAL: 2

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;www.zmailtech.com.             IN      A

;; ANSWER SECTION:
www.zmailtech.com.      86400   IN      CNAME   master.zmailtech.com.
master.zmailtech.com.   86400   IN      A       192.168.10.2

;; AUTHORITY SECTION:
zmailtech.com.          86400   IN      NS      ns1.zmailtech.com.

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

;; Query time: 2 msec
;; SERVER: 192.168.10.2#53(192.168.10.2)
;; WHEN: Thu Dec 14 13:18:19 IST 2017
;; MSG SIZE  rcvd: 117

[root@master ~]#

Now we test CNAME Record ftp.zmailtech.com via dig command  
 
[root@master ~]# dig ftp.zmailtech.com

; <<>> DiG 9.9.4-RedHat-9.9.4-50.el7 <<>> ftp.zmailtech.com
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 31273
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 1, ADDITIONAL: 2

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;ftp.zmailtech.com.             IN      A

;; ANSWER SECTION:
ftp.zmailtech.com.      86400   IN      CNAME   master.zmailtech.com.
master.zmailtech.com.   86400   IN      A       192.168.10.2

;; AUTHORITY SECTION:
zmailtech.com.          86400   IN      NS      ns1.zmailtech.com.

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

;; Query time: 0 msec
;; SERVER: 192.168.10.2#53(192.168.10.2)
;; WHEN: Thu Dec 14 13:19:01 IST 2017
;; MSG SIZE  rcvd: 117

[root@master ~]#

Now we test CNAME Record smtp.zmailtech.com via dig command 

[root@master ~]# dig smtp.zmailtech.com

; <<>> DiG 9.9.4-RedHat-9.9.4-50.el7 <<>> smtp.zmailtech.com
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 7689
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 1, ADDITIONAL: 2

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;smtp.zmailtech.com.            IN      A

;; ANSWER SECTION:
smtp.zmailtech.com.     86400   IN      CNAME   master.zmailtech.com.
master.zmailtech.com.   86400   IN      A       192.168.10.2

;; AUTHORITY SECTION:
zmailtech.com.          86400   IN      NS      ns1.zmailtech.com.

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

;; Query time: 0 msec

;; SERVER: 192.168.10.2#53(192.168.10.2)
;; WHEN: Thu Dec 14 13:19:12 IST 2017
;; MSG SIZE  rcvd: 118

[root@master ~]#