reverse, inverse, whats the diff?

Kevin Darcy kcd at
Wed Mar 29 22:17:51 UTC 2000

Duane Cox wrote:

> I have been using the term reverse as a synonym for inverse, but I don't think that is correct..
> Reverse being the ip to domain mapping done vi the domain..
> but what is inverse? same thing?

A reverse *zone* is one which maps addresses to domain names via PTR RR's.

An inverse *query* is one which asks the server to trace back all references it knows to a given
piece of data, e.g. all MX  RR's which point to a particular preference/target combination. See
RFC 1035 for details. One possible application of inverse queries would be to find out what A RR's,
if any, point to a particular address, which is an expensive simulation of a PTR lookup. Inverse
queries are deprecated.

- Kevin

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