rdns

README

rdns

rdns provides reverse DNS for IPv6 networks. It is a DNS server that serves PTR and AAAA records for an IPv6 subnet, and the corresponding authoritative NS records.

Setup

• Run rdns somewhere serving on port 53 (set flags appropriately).
• Ask your upstream IPv6 provider to create an ip6.arpa. NS record for your subnet that points to your rdns instance.
• Create an NS record for your subdomain (eg, v6.example.com) that also points to your rdns instance.

Command-line flags

rdns is configured with command-line flags:

  -domain string
        domain suffix for generated domain name (default ".v6.example.com.")
  -host_prefix string
        prefix for generated host name (default "ip-")
  -listen address
        DNS server listen address (default ":53")
  -network subnet
        subnet for which to serve ip6.arpa records (default "fe80::/64")
  -ns server
        name server for NS responses (default "ns.example.com.")
  -ttl seconds
        answer TTL in seconds (default 3600)

Demo

Here are a few dig queries against rdns running with its default flags:

$ dig -x fe80::f00d

;; QUESTION SECTION:
;d.0.0.f.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.8.e.f.ip6.arpa. IN PTR

;; ANSWER SECTION:
d.0.0.f.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.8.e.f.ip6.arpa. 3600 IN PTR ip-f00d.v6.example.com.


$ dig -t AAAA ip-f00d.v6.example.com

;; QUESTION SECTION:
;ip-f00d.v6.example.com.                IN      AAAA

;; ANSWER SECTION:
ip-f00d.v6.example.com. 3600    IN      AAAA    fe80::f00d


$ dig -t NS 0.0.0.0.0.0.0.0.0.0.0.0.0.8.e.f.ip6.arpa.

;; QUESTION SECTION:
;0.0.0.0.0.0.0.0.0.0.0.0.0.8.e.f.ip6.arpa. IN NS

;; AUTHORITY SECTION:
0.0.0.0.0.0.0.0.0.0.0.0.0.8.e.f.ip6.arpa. 3600 IN NS ns.example.com.

Acknowledgements

I made this because I wanted to serve reverse DNS for my IPv6 subnet. The first option I tried was AllKnowingDNS, for which there is a package on my Debian system, but it failed with a Perl runtime error due to a missing method on some object. Rather than try to debug Perl code I took the opportunity to learn more about DNS and write my own. It was a very informative experience, and was quite straightforward thanks to Miek Gieben's excellent dns package.

Copyright and License

This code is Copyright 2022 Google Inc. and is Apache 2.0 licensed.

Documentation

Overview

rdns is a DNS server that serves PTR and AAAA records for an IPv6 subnet, as well as the associated authoritative NS records.