DNS testing ground based on twisted.

Brought forward on Hack4Glarus 2019 -- Winter Edition with help from @anotherkamila, @fnux and @evilham.

Assign a zone to your /64 block and give friendly names like:

academy-podium-medical.yggdrasil.ungleich.cloud

to your jails, virtual machines, self-hosted services, ...

This is deployed for the yggdrasil experimental network on yggdrasil.ungleich.cloud.

In order to get a name assigned to you, execute from an yggdrasil enabled system:

curl "http://[204:504b:aea1:a6c6:453e:939f:ac70:1515]/register?domain=yggdrasil.ungleich.cloud"

This operation is idempotent and the three words are derived from your client's IP address (*).

(*): Since the space of words is significantly smaller than that of IPs, this service requires some state and assigns the combination of words on a first-come first-served basis. The algorithm further iterates to try to find a name for an IP but makes no promises of this being possible. Do host your own!

Use this to, for example, echo back an IPv4 as an A record on IPv6-only environments that have DNS64 and NAT64 setup. That way, your local DNS will add AAAA records that will enable your IPv6-only machines to connect to raw IPv4 addresses without domain.

This is deployed on echo.dnslab.evilham.com(**), use like this:

`host 127.0.0.8.echo.dnslab.evilham.com`

That will return an A record with 127.0.0.8 as an address. In DNS64+NAT64 environemnts you'll also see a AAAA record with 127.0.0.8 embedded in your NAT64's IPv6 prefix.

UPDATE: because reasons this also supports v6 now. As an alternative to ':' in v6, you can use '-' or '.'. Enjoy. (reasons: https://ungleich.ch/u/blog/has-a-name-for-every-ipv6-address/)

(**): Hosted on a best-effort basis :-). Host your own if you want to depend on it.