NAPTR Record - Rationale

Rationale

Uniform Resource Names (URNs) are a subset of Uniform Resource Identifiers (URIs) used for abstract identifiers, such as a person's name or their telephone number. For URNs to be meaningful, they must be mapped to a concrete resource of some sort. Uniform Resource Locators (URLs) are often used to describe such resources, such as a computer hostname, or a local file.

As part of the standardization of URNs, NAPTR records were introduced to do just this. NAPTR records map between sets of URNs, URLs and plain domain names and suggest to clients what protocol should be used to talk to the mapped resource. Each NAPTR record contains a service name, a set of flags, a regexp rule, an order value, a preference and a replacement. Multiple records can be chained together in a cascade to rewrite URIs in fairly sophisticated, but deterministic ways. These cascading rules have been standardized in RFC2915 and RFC3403.