Resolution of Uniform Resource Identifiers using the Domain Name System

摘要

Uniform Resource Locators (URLs) are the foundation of the World WideWeb, and are a vital Internet technology. However, they have provento be brittle in practice. The basic problem is that URLs typicallyidentify a particular path to a file on a particular host. There isno graceful way of changing the path or host once the URL has beenassigned. Neither is there a graceful way of replicating the resourcelocated by the URL to achieve better network utilization and/or faulttolerance. Uniform Resource Names (URNs) have been hypothesized as aadjunct to URLs that would overcome such problems. URNs and URLs areboth instances of a broader class of identifiers known as UniformResource Identifiers (URIs).The requirements document for URN resolution systems[15] defines theconcept of a "resolver discovery service". This document describesthe first, experimental, RDS. It is implemented by a new DNS ResourceRecord, NAPTR (Naming Authority PoinTeR), that provides rules formapping parts of URIs to domain names. By changing the mappingrules, we can change the host that is contacted to resolve a URI.This will allow a more graceful handling of URLs over long timeperiods, and forms the foundation for a new proposal for UniformResource Names.In addition to locating resolvers, the NAPTR provides for othernaming systems to be grandfathered into the URN world, providesindependence between the name assignment system and the resolutionprotocol system, and allows multiple services (Name to Location, Nameto Description, Name to Resource, ...) to be offered. In conjunctionwith the SRV RR, the NAPTR record allows those services to bereplicated for the purposes of fault tolerance and load balancing.