How to get a free .arpa domain

The .arpa top-level domain is reserved for critical internet infrastructure and isn't open to public registration, so you can't own a normal mysite.arpa. However, some subdomains are effectively user-controllable: e164.arpa, for example, lets people in Germany and the Czech Republic set DNS records for their phone numbers. For everyone else, a similar opportunity exists under ip6.arpa, which is intended for reverse DNS lookups (turning IPv6 addresses into names) but whose specification doesn't forbid other uses.

To claim one, you sign up for a free account on Hurricane Electric's tunnelbroker.net (fake info is fine). Under 'Create Regular Tunnel,' you provide any IPv4 endpoint that responds to ICMP pings; the site doesn't verify you control the address. The author pinged news.ycombinator.com and got 209.216.230.207, which passed validation. After choosing any tunnel server, you receive a Routed IPv6 Prefix such as 2001:470:1f09:140::/64. Taking everything before the trailing colons (2001:470:1f09:140), you pad each group to four characters (2001:0470:1f09:0140), insert dots between every character, reverse the whole string, and append .ip6.arpa — yielding e.g. 0.4.1.0.9.0.f.1.0.7.4.0.1.0.0.2.ip6.arpa.

For DNS hosting, Cloudflare rejected the domain, but deSEC accepted it. After adding the .ip6.arpa address on deSEC, you go back to Tunnelbroker and change your rDNS delegation to deSEC's nameservers. The result is a fully functional website under a free .arpa domain.