DNS provides a means for associating domain names with IP addresses. A system of DNS servers operating on the Internet delivers the seamless address mapping that lets you surf the web with names instead of numbers. But what if you have a very small network that resides behind a firewall with network address translation? A simple local network doesn't need anything close to the functionality provided by a full-blown DNS implementation. Typically, it is quite enough to respond to DNS requests from hosts on the local network and forward all other requests to the provider's DNS server.

Dnsmasq is a simple, lightweight implementation of DNS, DHCP, and TFTP for small, local networks. This practical tool serves up addresses for the local network and forwards requests for external hosts to any DNS server. Because Dnsmasq integrates DNS with DHCP, it remembers the names of hosts that receive addresses through DHCP. This approach significantly reduces configuration time. All you need to do is set up each client to use DHCP, and you won't need to maintain an /etc/hosts file for hostname-to-address mapping. The program is frugal in its use of resources, and it is therefore well suited for deployment on Linux-based router systems.

Several popular Linux distributions have Dnsmasq in their repositories. On Debian, Ubuntu, and openSUSE, you need to install the dnsmasq package. The popular router distributions OpenWrt, DD-WRT, and FreeWRT all include the program [1] [2]. In our lab, Dnsmasq ran on Debian from a USB stick attached to an Asus WL-500g Premium DSL router (Figure 1) [3].

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