Because all DNS software is supposed to know that the .arpa domain name is managed by the IETF and not ICANN. Or, rather, they know not to try to resolve it. Th

Because all DNS software is supposed to know that the .arpa domain name is managed by the IETF and not ICANN. Or, rather, they know not to try to resolve it. There are a handful of different .arpa domains in use, and they all require special handling from your DNS server. E.g. reverse DNS/rDNS uses in-addr.arpa., and the DNS server in even the dumbest consumer-grade router will know how to respond to requests under that domain.