LAB: Configure a DNS service.

Installing a DNS service will bring you several advantages:
– you define machine names one for all in a centralized way, you can then better organize your workshops, build machines dedicated to a specific task (NFS server, LDAP server, etc),
– you don’t need to regularly edit the /etc/hosts file of each of them,
– you can use the machine names everywhere in an efficient way,
– you can now test postfix labs: this only point makes DNS service mandatory.

Besides making conversion between IP address and names, the DNS service provides the infrastructure necessary for mail management through the MX records.

Let’s install a DNS server for the example.com domain.
Install the bind package:

# yum install -y bind

Edit the /etc/named.conf file and change the ‘listen-on‘ option from 127.0.0.1 to any:

listen-on port 53 { any; };

In the same file, change the ‘allow-query‘ option from localhost to any:

allow-query { any; };

In the same file, disable the ‘dnssec-validation‘ option:

dnssec-validation no;

Still in the same file, below the ‘recursion‘ option, add the two following lines (with 192.168.1.1 being the DNS IP address of your Internet provider):

forward only;
forwarders { 192.168.1.1; };

In the same file, add the following lines at the end:

zone "example.com" {
 type master;
 file "example.com.zone";
 allow-update { none; };
};

zone "1.168.192.in-addr.arpa" {
 type master;
 file "example.com.revzone";
 allow-update { none; };
};

Go to the /var/named directory:

# cd /var/named

Create the example.com.zone file and add the following lines:

$TTL 86400
@ IN SOA master.example.com. root.example.com. (
 2013110101 ; Serial
 1d ; refresh
 2h ; retry
 4w ; expire
 1h ) ; min cache
 IN NS master.example.com.
 IN MX 10 postfix.example.com.

gateway IN A 192.168.1.1
master IN A 192.168.1.5
postfix IN A 192.168.1.10

Create the example.com.revzone file and add the following lines:

$TTL 86400
@ IN SOA master.example.com. root.example.com. (
 2013110102 ; Serial
 1d ; refresh
 2h ; retry
 4w ; expire
 1h ) ; min cache
 IN NS master.example.com.

1 IN PTR gateway.example.com.
5 IN PTR master.example.com.
10 IN PTR postfix.example.com.

Check the configuration files:

# named-checkconf

Note: don’t forget to increment the serial number (in bold in the files above) each time you change something before reloading the named service.

Set the DNS configuration:

# system-config-network

Choose ‘DNS configuration‘, then type:

Hostname: master.example.com
Primary DNS: 192.168.1.5
DNS search path: example.com

Type ‘OK‘, then ‘Save&Quit‘.

Add two new rules to the firewall configuration:

# iptables -I INPUT -m state --state NEW -m tcp -p tcp --dport 53 -j ACCEPT
# iptables -I INPUT -m state --state NEW -m udp -p udp --dport 53 -j ACCEPT

Save the firewall configuration:

# service iptables restart

Activate the DNS service:

# chkconfig named on

Start the DNS service:

# service named start

Check the configuration:

# nslookup master.example.com
# nslookup 192.168.1.5