Apparently .aero originally reserved all three letter domains for IATA codes, but only a couple hundred airports took them up on it https://www.information.aero/airports_codes_released
For a sense of scale on 'only 227 registered one', there are currently 9161 IATA airport codes
@iliana@cybre.space I too wish the netfilter project promised a stable API (https://netfilter.org/documentation/FAQ/netfilter-faq-4.html#ss4.5)