Reverse domain name notation

Reverse-DNS strings are based on registered domain names, with the order of the components reversed for grouping purposes.

Reverse-DNS names are a simple way of eliminating namespace collisions, since any registered domain name is globally unique to its owner (with alt roots making exceptions to this rule possible but unlikely).

The first appearance of reversed DNS strings predated the Internet domain name standards.

The UK Joint Academic Networking Team (JANET) used this order in its Name Registration Scheme, before the Internet domain name standard was established.

During the period while both JANET-style and Internet-style addresses were in use, mailers and gateway sites had ad-hoc workarounds to handle the differences, but could still be confused.