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How to Setup a DNS Server in Ubuntu

Would you like to setup a DNS Server in Ubuntu? How about setting up aprivate internal domain name at home? Well, you’ve come to the rightplace. There are number of tutorials on the internet showing you how tosetup a DNS Server with Ubuntu using Bind 9. So, why another how-todocument? That’s a good question. I’ve decided I needed to write asimple tutorial that anyone with a little bit of Linux knowledge wouldbe able to follow. In the process, I hope readers are also able tolearn how DNS works. Ok, let’s jump right to it!

What is DNS?

First of all, let’s cover the basics. What is DNS? DNS stands forDomain Name Server. It’s a service that runs on a server thattranslates humanly recognizable domain names such as www.yahoo.com orwww.google.com into its assigned IP addresses. If the DNS server doesnot recognize the domain name being requested, it will forward thedomain name request to another DNS server and so on until the name isresolved.

A typical DNS request is when someone is accessing a website. Let’suse the www.yahoo.com domain as an example. When a user clicks a Yahoolink or types the Yahoo URL on the address bar of the browser, the DNSserver processes the domain request. If it doesn’t find www.yahoo.comon its DNS table, it will forward the request to another DNS serverwith a higher authority and so on until it finds a server with the URLentry. The IP address information is then sent back to the user’sbrowser. If the domain name is not found, a “server not found” messageis displayed on the browser.

Assumptions

Enough with the DNS background. Let’s now start configuring our ownDNS server. Let’s assume that we have the following: we want to createa private internal domain name called mydomain.com, our private internal network is 192.168.0.x and our router and gateway is set at 192.168.0.1. Let’s assume all devices are going to be configured with static IP addresses.Normally, most computer systems nowadays are configured toautomatically obtain IP addresses from the DHCP server/router. In thisexample, we will use static IP addresses to show how DNS works.Finally, we have 3 computers connected to our network:

• Ubuntu Server, the DNS server – 192.168.0.9
• Ubuntu Desktop – 192.168.0.10
• PC – 192.168.0.11

Instructions

1. To install the DNS server, we need to install Bind 9.

sudo apt-get install bind9

2. Let’s configure Bind. We need to touch 5 files.

We will edit 3 files.

• /etc/bind/named.conf.local
• /etc/bind/named.conf.options
• /etc/resolv.conf

We will create 2 files.

• /etc/bind/zones/mydomain.com.db
• /etc/bind/zones/rev.0.168.192.in-addr.arpa

A. First step. Lets add our domain zone – mydomain.com.

sudo vi /etc/bind/named.conf.local

# Our domain zone
zone "mydomain.com" {
   type master;
   file "/etc/bind/zones/mydomain.com.db";
};
 
# For reverse DNS 
zone "0.168.192.in-addr.arpa" {
   type master;
   file "/etc/bind/zones/rev.0.168.192.in-addr.arpa";
};

Save file. Exit.

We just created a new domain. Please note: later we will create twofiles named mydomain.com.db and rev.0.168.192.in-addr.arpa files. Also,notice the reverse IP address sequence in the reverse DNS section.

B. Let’s add the DNS servers from your ISP. In my case, I’m usingComcast DNS servers. You can place the primary and secondary DNSservers here separated by semicolons.

sudo vi /etc/bind/named.conf.options

forwarders {
   68.87.76.178;
};

Save file. Exit.

C. Now, let’s modify the resolv.conf file found in /etc and place the IP address of our DNS server which is set to 192.168.0.9.

$ sudo vi /etc/resolv.conf

search mydomain.com.
nameserver 192.168.0.9

D. Now, let’s define the zones.

sudo mkdir /etc/bind/zones
sudo vi /etc/bind/zones/mydomain.com.db

$TTL 3D
@ IN SOA ns.mydomain.com. admin.mydomain.com. (
   2007062001
   28800
   3600
   604800
   38400
);
mydomain.com.  IN      NS         ns.mydomain.com.
ubuntudesktop  IN      A          192.168.0.10
www            IN      CNAME      ubuntudesktop
pc             IN      A          192.168.0.11
gw             IN      A          192.168.0.1
                       TXT        "Network Gateway"

The TTL or time to live is set for 3 days
The ns.mydomain.com nameserver is defined
ubuntudesktop, pc and gateway are entered as an A record
An alias of www is assigned to ubuntudesktop using CNAME

E. Let’s create a “rev.0.168.192.in-addr.arpa” file for reverse lookup.

sudo vi /etc/bind/zones/rev.0.168.192.in-addr.arpa

$TTL 3D
@       IN      SOA     ns.mydomain.com. admin.mydomain.com. (
                2007062001
                28800
                604800
                604800
                86400
)
        IN      NS      ns.mydomain.com.
1       IN      PTR     gw.mydomain.com.
10      IN      PTR     ubuntudesktop.mydomain.com.
11      IN      PTR     pc.mydomain.com.

3. Let’s restart Bind to activate our latest changes.

sudo /etc/init.d/bind9 restart

4. Finally, let’s test our new domain and DNS entries.

Dig

$ dig mydomain.com

Nslookup

nslookup gw

5. That’s it.