rust-dns

Good morning! This is a toy for playing with DNS. It can do a few things:

• Run an DNS echo server (that can be queried using dig)
• Read DNS packets stored on disk

This is a playground to improve my understanding of DNS at the packet level, so I can implement an embedded nameserver in another project. I'm making it public in case it's useful for others :)

On the roadmap:

• DNS server that HTTP clients can resolve against
  • i.e. a (local) authoritative nameserver
• TCP support
• Tests

Usage

Reading a packet from file

Using an example file

$ cargo run --bin cli -- read examples/question_packet
$ ...

Generating your own DNS packet

First, listen on a port using netcat:

$ nc -u -l 3000 > question_packet

Then, in a seperate terminal, make a DNS request to it using dig:

$ dig +retry=0 -p 3000 @127.0.0.1 +noedns example.com

When this completes, you can stop the netcat server and parse the datagram:

$ cargo run --bin cli -- read question_packet
$ ...

Run a DNS echo server

This will receive UDP packets, parse and print them, and then echo them back to the caller.

$ cargo run --bin cli -- serve 127.0.0.1:3000
$ dig +retry=0 -p 3000 @127.0.0.1 +noedns example.com

Project structure

• /cli contains the commandline interface and UDP server
• /core contains the DNS packet parsing logic

References

• Domain names (RFC 1035, 1987)
• How DNS works (Julia Evans, 2021)
• DNS Guide (Emil Hernvall, 2017)