How to Setup a DNS Server in Ubuntu

Overview
Would you like to setup a DNS Server in Ubuntu? How about setting up a private internal domain name at home? Well, you’ve come to the right place. There are number of tutorials on the internet showing you how to setup a DNS Server with Ubuntu using Bind 9. So, why another how-to document? That’s a good question. I’ve decided I needed to write a simple tutorial that anyone with a little bit of Linux knowledge would be able to follow. In the process, I hope readers are also able to learn 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 for Domain Name Server. It’s a service that runs on a server that translates humanly recognizable domain names such as www.yahoo.com or www.google.com into its assigned IP addresses. If the DNS server does not recognize the domain name being requested, it will forward the domain name request to another DNS server and so on until the name is resolved.

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

Assumptions
Enough with the DNS background. Let’s now start configuring our own DNS server. Let’s assume that we have the following: we want to create a 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 to automatically obtain IP addresses from the DHCP server/router. In this example, 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.

1. $ sudo apt-get install bind9  

$ 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.

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

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

1. # Our domain zone  
2. zone "mydomain.com" {  
3.    type master;  
4.    file "/etc/bind/zones/mydomain.com.db";  
5. };  
6.   
7. # For reverse DNS   
8. zone "0.168.192.in-addr.arpa" {  
9.    type master;  
10.    file "/etc/bind/zones/rev.0.168.192.in-addr.arpa";  
11. };  

# 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 two files 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 using Comcast DNS servers. You can place the primary and secondary DNS servers here separated by semicolons.

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

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

1. forwarders {  
2.    68.87.76.178;  
3. };  

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.

1. $ sudo vi /etc/resolv.conf  

$ sudo vi /etc/resolv.conf

1. search mydomain.com.  
2. nameserver 192.168.0.9  

search mydomain.com. nameserver 192.168.0.9

D. Now, let’s define the zones.

1. $ sudo mkdir /etc/bind/zones  
2. $ sudo vi /etc/bind/zones/mydomain.com.db  

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

1. $TTL 3D  
2. @ IN SOA ns.mydomain.com. admin.mydomain.com. (  
3.    2007062001  
4.    28800  
5.    3600  
6.    604800  
7.    38400  
8. );  
9. mydomain.com.  IN      NS         ns.mydomain.com.  
10. ubuntudesktop  IN      A          192.168.0.10  
11. www            IN      CNAME      ubuntudesktop  
12. pc             IN      A          192.168.0.11  
13. gw             IN      A          192.168.0.1  
14.                        TXT        "Network Gateway"  

$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.

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

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

1. $TTL 3D  
2. @       IN      SOA     ns.mydomain.com. admin.mydomain.com. (  
3.                 2007062001  
4.                 28800  
5.                 604800  
6.                 604800  
7.                 86400  
8. )  
9.         IN      NS      ns.mydomain.com.  
10. 1       IN      PTR     gw.mydomain.com.  
11. 10      IN      PTR     ubuntudesktop.mydomain.com.  
12. 11      IN      PTR     pc.mydomain.com.  

$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.

1. $ sudo /etc/init.d/bind9 restart  

$ sudo /etc/init.d/bind9 restart

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

Dig

1. $ dig mydomain.com  

$ dig mydomain.com

Nslookup

1. $ nslookup gw  

$ nslookup gw

5. That’s it.