DNS: Create a Reverse Zone File

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DNS: Create a Reverse Zone File

Creating reverse zones is crucial to DNS server configuration, and in performing reverse name service lookups. In this video, we will see how to configure the zone in `/etc/named.conf` and create the Start of Authority record as well as other records in the reverse zone file. Then we'll test our configuration with a reverse query.

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Lab Info

Level

Intermediate

Last updated

Aug 10, 2025

Duration

30m

Challenge

Get the IP Address for the Primary Interface for the Lab Server
Record the IP address for the primary interface:
```
ifconfig -a
```
Challenge

Add the Reverse Zone Configuration to the /etc/named.conf File. Then Run the named-checkconf Command to Verify the Configuration
```
vim /etc/named.conf
```
Take the last three octets of the public IP address and enter them in reverse where you see xx.xx.xxx (such as 11.31.172). Insert the zone configuration just before the include statements at the bottom of the file:
```
zone "xx.xx.xxx.in-addr.arpa" {
   type master;
   file "/var/named/xx.xx.xxx.db";
}
```
Then run the named-checkconf command to verify the configuration.
```
named-checkconf
```

Challenge

Create the Reverse Zone File and Check the Configuration for Syntax Errors with named-checkzone

Create the reverse zone file and enter the following information:
```
vim /var/named/xx.xx.xxx.db
```

Enter in the following:

$TTL    86400
@       IN      SOA     nameserver.mylabserver.com. root.mylabserver.com. (
                          10030         ; Serial
                           3600         ; Refresh
                           1800         ; Retry
                         604800         ; Expiry
                          86400         ; Minimum TTL
)
; Name Server
@        IN      NS       nameserver.mylabserver.com.
; PTR Record Definitions
93       IN      PTR       nameserver.mylabserver.com.
30       IN      PTR       mailprod.mylabserver.com.
72       IN      PTR       mailbackup.mylabserver.com.
; Mail Exchange Records
@		IN	MX	10	mailprod.mylabserver.com.
@		IN	MX	20	mailbackup.mylabserver.com.

Run the named-checkzone command to check the zone file for syntax errors.
```
named-checkzone mylabserver.com xx.xx.xxx.db
```

Challenge

Change the File Permissions and the Group Owner for /var/named/xx.xx.xxx.db
1. Change the file permissions for /var/named/xx.xx.xxx.db:
  chmod 760 /var/named/xx.xx.xxx.db
2. Change the group owner of the file to named:
  chgrp named /var/named/xx.xx.xxx.db
Challenge

Restart the named Service
```
systemctl restart named
```
Challenge

Run a Query to Test the Configuration
```
nslookup x.x.x.x localhost
```
Replace x.x.x.x with what ifconfig -a returned for an IP address earlier.

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