dns-server

A Simple DNS proxy server for IPv6 with caching and logging, written in C.

• Listens for DNS requests (in binary ".raw" packets) for IPv6 addresses over TCP (not UDP), on port 8053
• Forwards each request to another DNS server provided as arguments (e.g. Google's 8.8.8.8, port 53)
• Caches 5 most recent queries, forgoing the request forwarding if responding from cache is possible.
• Logs server events in the file ./dns_svr.log.

Notes:

• Depends on POSIX libraries, so this will not run on Windows (use WSL)
• Not multithreaded, this server blocks when forwarding each request

Running the program

Compile with GCC (at least C99) using

make

then run

./dns_svr <hostname> <port>

to start the server, passing in the details of the upstream server to forward DNS requests and replies.

For testing, it is possible to use Google's public DNS:

• hostname 8.8.8.8
• port 53

Usage

Ensure the server is running (locally), listening for TCP on 8053:

./dns_svr 8.8.8.8 53

On UNIX systems, dig can be used as a DNS client (so no manual writing/reading of DNS request/reply packets is needed).

Though you can examine/modify each DNS-over-TCP packet with Wireshark if you want to. Hexdumping on the command line with od, like od -Ax -tx1 -v 1.req.raw > dump is also possible.

Examples

Requesting the IPv6 (hence AAAA) address of 'cloudflare.com' over TCP, from the server 0.0.0.0 on port 8053, i.e. dns-server running locally.

dig +tcp @0.0.0.0 -p 8053 AAAA cloudflare.com

The log file ./dns_svr.log will record the request and the reply, with a timestamp.