Dnsmasq is a lightweight, easy to configure, DNS forwarder and DHCP server. It is designed to provide DNS and optionally, DHCP, to a small network. It can serve the names of local machines which are not in the global DNS. The DHCP server integrates with the DNS server and allows machines with DHCP-allocated addresses to appear in the DNS with names configured either in each host or in a central configuration file. Dnsmasq supports static and dynamic DHCP leases and BOOTP for network booting of diskless machines.

Basic DNS Setup

First things first, lets install the package:

aptitude update
aptitude install dnsmasq

If your goal was to set up a simple DNS server, you just succeeded. To test it, use your favorite DNS lookup tool pointed at localhost.

dig debian.org @localhost

or

nslookup debian.org localhost

By default, DNS is configured to forward all requests to your system's default DNS settings. In case you didn't know, these are stored in the /etc/resolv.conf file. (See ["HowTo/networking"] or type "man resolv.conf" for more details.

Now, if you want to add some names for your DNS server to resolve for your clients, simply add them to your /etc/hosts file.

Choosing Your Interfaces

One you will probably want to do is tell dnsmasq which ethernet interface it can and cannot listen on, as we really don't want it listening on the internet. Around line 69, you will see:

#interface=

Uncomment the line and specify which ethernet interface(s) you want it server IPs to. For example, if I want it to listen on eth1 (my DMZ) and eth2 (my local network), then it should look like:

interface=eth1
interface=eth2

If I didn't edit this line, it would also listen on eth0, my internet connection. I personally wouldn't recommend this, as it gives those evil guys a few doors to try to break into.

Basic DHCP Setup

By default, DHCP is turned off. This is a good thing, as you could bring down whatever network you are connected to if you are not careful.

To enable it, there is at least one line will need to edit in the /etc/dnsmasq.conf file. Around line 143, you will see:

#dhcp-range=192.168.0.50,192.168.0.150,12h

To enable the DHCP server, you will need to give it a range of IP addresses to hand out. In the example above, this server would hand out 101 address starting at 192.168.0.50 and ending at 192.168.0.150. The last number is how long the DHCP leases are good for. In this example, they would be good for twelve hours.

Since we have two different networks that need DHCP, we are going to change that line to:

dhcp-range=eth1,192.168.100.100,192.168.200.199,4h
dhcp-range=eth2,192.168.200.100,192.168.200.199,4h

Now restart your dnsmasq server, connect up a few clients, and see if they autoconfigure themselves.

/etc/init.d/dnsmasq restart