Reverse mapping

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In the Domain Name Service (DNS), reverse mapping is the function that, when given an Internet Protocol version 4 or an Internet Protocol version 6 address, returns an associated domain name.

When a block of address space is assigned by an address registry or upstream provider, there is usually a mapping for the entire block, which links to a database at an address registry. This database will provide administrative information about the recipient of the allocation, such as receiving organization, and its technical and administrative contacts.

In configuring DNS, where type A (IPv4) or AAAA (IPv6) resource records (RR) do name-to-address forward mapping, type PTR RRs describe the reverse mapping.