The DNSMasq is a service that combines DNS and DHCP in an elegant and easy to configure way. It’s focus is to consume as little memory resources and disk space as possible, therefore it’s highly recommended for simple networks with only a couple of hosts.

With those characteristics, it’s very common to see it being used on Linux distributions aimed at home routers, like the OpenWrt or DD-WRT. For the same reason, it’s also perfect to be run on a Raspberry Pi.

In this post I’ll run through and explain a simple configuration that I have used for my local network.

The DNSMasq is available as a .deb package for the Raspbian, so it can be installed through an apt-get:

$ sudo apt-get install dnsmasq

The main configuration file is on /etc/dnsmasq.conf. It’s possible to write the whole configuration directly in it, nonetheless, it’s better to create new files in the /etc/dnsmasq.d directory for organization. In order for this to be possible, it’s necessary to uncomment the last line of the /etc/dnsmas.conf file:

# Include a another lot of configuration options.
#conf-file=/etc/dnsmasq.more.conf
conf-dir=/etc/dnsmasq.d

From now on, every text file created on /etc/dnsmasq.d will be used as the service configuration:

$ sudo vi /etc/dnsmasq.d/network.conf

I have used network.conf for the filename, but anything else is fine.

The first step is to configure a domain name. It’s defined in the domain option:

domain=raspberry.local

This domain dame will be accessible only locally and through this DNS server.

By default, the DNSMasq will use the nameserver addresses defined in the /etc/resolve.conf as the outside DNS Servers. But there is also the no-resolv option that disables that behaviour and then it’s possible to configure the DNS manually:

no-resolv
server=208.67.222.222
server=208.67.220.220

I have used the OpenDNS instead of the DNS provided by my ISP. GoogleDNS is also another good option.

For more configurations on the DNS service, consult the DNSMasq manual page.

Following the DNS configuration, we follow on to the DHCP configuration. The first configuration is the dhcp-range that defines a range of IP addresses that are going to be distributed among the clients when joining the network:

dhcp-range=10.0.0.50,10.0.0.59,120m

In this case, the server will assign addresses from 10.0.0.50 up to 10.0.0.59, inclusive. It’s important to adjust the range according to how many devices will be connected to the network simultaneously.

It’s also important to notice the 120m value configured together with the address range. This value is the lease time for this range.

The lease time configuration is something that varies with application. The most usual value is 24h, which is already pretty adequate for most home networks. Shorter periods are usually used for public WiFi networks, like in stores and restaurants, where there is a great rotation of clients accessing the network.

After defining the DHCP range and the lease time, we can define the default gateway that will be advertised to the clients:

dhcp-option=option:router,10.0.0.254
dhcp-authoritative

There is no direct configuration for the default gateway but it’s possible to use the dhcp-option, which directly sets DHCP options that will be advertised.

The first argument is the option value, according to the RFC 2132 (or this IANA page) directly or the enum option:router. The seccond argument is the value that will be advertised. In this case 10.0.0.254, which is the IP address of the ISP’s modem/routers.

Finally, the dhcp-authoritative is to indicate that this is the main DHCP server of the network.

For more options on how to configure the DHCP, consult the DNSMasq manual page.

After writing and saving the configuration file, it’s necessary to restart the dnsmasq service and everything is ready to be used:

$ sudo service dnsmasq restart

Fixed Address Hosts

Since there is a limited IP address range being distributed with limited lease time, it’s inevitable that sooner or later the address advertised for a certain device will be different.

Usually this is not a problem, but in certain situations it’s important to define fixed IP addresses for certain elements. The most common cases in a domestic network are file servers or printers, but they can also be necessary for setting up NAT Port Forwarding.

To create a fixed address host we use the dhcp-host configuration:

# My Computer
dhcp-host=AA:BB:CC:DD:EE:FF,mycomputer,10.0.0.1,infinite

# Print Server
dhcp-host=00:11:22:33:44:55,printer,10.0.0.2,infinite

In this case, the 10.0.0.1 is reserved for the device with AA:BB:CC:DD:EE:FF MAC address.

Notice that the lease time used is infinite, meaning that the host will never change the IP address. It’s also possible to define limited leases, but it doesn’t make much sense.

Also notice that the addresses are not in the other DHCP range.

Something that is very interesting in the DNSMasq is that by specifying a hostname for a fixed address device, it will be already included in the DNS service. Following the example, next time it’s necessary to connect to the printer from a PC, instead of pointing to 10.0.0.2, it’s possible to access printer.raspberry.local (remember the domain name configured in the beginning):

~$ host printer.raspberry.local
printer.raspberry.local has address 10.0.0.2

~$ ping printer.raspberry.local
PING printer (10.0.0.2) 56(84) bytes of data.
64 bytes from printer (10.0.0.2): icmp_seq=1 ttl=64 time=1.45 ms
64 bytes from printer (10.0.0.2): icmp_seq=2 ttl=64 time=0.144 ms
 --- printer ping statistics ---
2 packets transmitted, 2 received, 0% packet loss, time 1001ms
rtt min/avg/max/mdev = 0.144/0.799/1.454/0.655 ms

References

1. DNSMasq Man Page
2. Hey Stephen Wood’s English Tutorial (Focused on DNS Caching)
3. Raspberry Pi Forum Post