Ubuntu DNS Server

This article is part of a series on setting up an Ubuntu Network Server. Below are the other sections of the article.

• Ubuntu Network Server
• Ubuntu DNS Server
• Ubuntu DHCP Server
• Ubuntu Firewall and Router
• Ubuntu File Server

First, run the following to install the software for the DNS server.

sudo apt-get install bind9

Edit the file /etc/bind/named.conf.local. Remove all of the contents and add the following:

zone "shortround.net" {
    type master;
    file "/etc/bind/zones/shortround.net";
};

zone "100.168.192.in-addr.arpa" {
    type master;
    file "/etc/bind/zones/100.168.192.in-addr.arpa";
};

Make sure you substitute shortround.net with your domain name and also substitute 100.168.192 with your subnet. Notice, the subnet is ordered backwards from they way you are probably used to.

Next, edit the /etc/bind/named.conf.options file. Uncomment the forwarders section and make it look like mine below. The forwarders are the DNS servers to query when our DNS server does not know how to resolve an address. I used OpenDNS for my servers.

forwarders { 
    208.67.222.222;
    208.67.220.220;
};

Lastly, we need to create our zone files. The first file is used to turn a domain name into an IP address. Edit the file /etc/bind/zones/shortround.net and add the following:

$TTL 1D
@       IN      SOA     kiev    root (
                                45;
                                1D;
                                6H;
                                40D;
                                1D);
                NS      kiev
biggles         A       192.168.100.20
giap            A       192.168.100.21
gimli           A       192.168.100.22
mail            CNAME   ghs.google.com.
kiev            A       192.168.100.1
squirt          A       192.168.100.23
www             A       8.12.37.105

Make sure to substitue any instance of kiev to the hostname of your server. Note that this DNS server handles all of the requests for your domain. If it can't find an address for the domain, it just stops there. This is a problem if you use the same domain name for your internal network as well as your web hosting. In the above file, I have to explicitly point the www domain to my hosting provider. I also use Google Apps for my email hosting, so I have to make a pointer to Google for their website to work correctly from my network.

The other zone file is /etc/bind/zones/100.168.192.in-addr.arpa. It is responsible for mapping IP addresses to domain names. Edit the file and add the following:

$TTL 1D
@       IN      SOA     kiev    root (
                                45;
                                1D;
                                6H;
                                40D;
                                1D);
                NS      kiev.shortround.net.
1               PTR     kiev.shortround.net.
20              PTR     biggles.shortround.net.
21              PTR     giap.shortround.net.
22              PTR     gimli.shortround.net.
23              PTR     squirt.shortround.net.

Again, make sure to substitute any instance of kiev to the hostname of your server.

We're now ready to test it out. First, restart the bind service.

sudo invoke-rc.d bind9 restart

There is a problem, though. Since our external interface is set dynamically, even if we tell our server to use its own domain name server, those settings will be lost the next time the interface is configured. To fix this, we need to modify the way the system handles its DHCP requests. Edit the /etc/dhcp3/dhclient.conf file and modify it as below.

supersede domain-name "shortround.net";
prepend domain-name-servers 127.0.0.1;
request subnet-mask, broadcast-address, time-offset, routers,
#       domain-name, domain-name-servers, host-name,
        netbios-name-servers, netbios-scope;

As always, you will have to modify this to fit your needs. What we've done is:

1. We forced the DHCP client to always use the "shortround.net" domain instead of the supplied one.
2. We forced the DHCP client to use our DNS server first.
3. We commented out the line that would normally give us the above settings that we forced.

Now restart your networking.

sudo invoke-rc.d networking restart

You should now be able to resolve internet addresses as well as local computer addresses.

One Last Note

It's best to keep your zone files cleaned up. Notice in the first file, all of the hosts are listed in alphabetical order. Also notice that the second file has all of the hosts listed in numeric order. Keep your records this way will greatly simplify an modifications that need done.

This was posted on Wednesday, August 27, 2008 at 10:34. It is filed under Ubuntu.
It is licensed under the Creative Commons Attribution 3.0 Unported License. View the markdown for this article.