SimpleDNS is a very simple DNS server written in C. It was made to learn the basics of the DNS protocol.

Features:

• very small
• single-threaded
• very simplistic memory management
• supports A, AAAA and TXT queries
• no full protection against invalid requests :|

git clone https://github.com/mwarning/SimpleDNS.git
cd SimpleDNS
make

Start SimpleDNS:

$./main
Listening on port 9000.

In another console execute dig to make a DNS request:

$ dig @127.0.0.1 -p 9000 foo.bar.com A
; <<>> DiG 9.8.4-rpz2+rl005.12-P1 <<>> @127.0.0.1 -p 9000 foo.bar.com
; (1 server found)
;; global options: +cmd
;; Got answer:
;; -&gt;&gt;HEADER&lt;&lt;- opcode: QUERY, status: NOERROR, id: 15287
;; flags: qr; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0
;; QUESTION SECTION:
;foo.bar.com. IN A
;; ANSWER SECTION:
foo.bar.com. 0 IN A 192.168.1.1
;; Query time: 0 msec
;; SERVER: 127.0.0.1#9000(127.0.0.1)
;; WHEN: Mon Apr 15 00:50:38 2013
;; MSG SIZE rcvd: 56

Note:

• On Debian Linux, dig is part of the dnsutils package.
• Use AAAA instead of A in the dig command line to request the IPv6 address.

The code maps the domain foo.bar.com to the IPv4 address 192.168.1.1 and IPv6 address fe80::1. It is easy to find it in the code and to add other entries.

The DNS section of the TCP/IP-Guide was very helpful for understanding the protocol.

• https://github.com/wfelipe/simple-dns