RFC1034 (November 1987, Domain Names - Concepts and Facilities) discusses the architecture of the DNS, and RFC1035 (November 1987, Domain Names— Implementation and Specification) spells out the implementation details.

Recognizing that the DNS is the only truly global Internet directory but that it could never support per-resource URL resolution, RFC2168 (June 1996, Resolution of Uniform Resource Identifiers, Using the Domain Name System) proposes a hybrid approach: a DNS resource record called Naming Authority Pointer (NAPTR) that maps parts of URIs to domain names. The idea is that a URN can refer, through DNS, to a resolver that produces an address.

LDAP’s purpose was to lower the “high cost-of-entry” that had prevented the widespread use of X.500-style directory services on the Internet. The core protocol is defined in a series that begins with RFC1487 (July 1993, X.500 Lightweight Directory Access Protocol) and ends with RFC2251 (December 1997, Lightweight Directory Access Protocol (v3)). RFC2252 (December 1997, Lightweight Directory Access Protocol (v3): Attribute Syntax Definitions) defines “the framework for developing schemas for directories accessible via the Lightweight Directory Access Protocol.” RFC2254 (December 1997, The String Representation of LDAP Search Filters) defines the LDAP query language illustrated in Chapter 14.

Despite LDAP’s success, the vision of a consolidated Internet white pages service remains elusive. There are many public LDAP directories, but none are authoritative, and there’s no real coordination among them. RFC1684 (August 1994, Introduction to White Pages Services Based on X.500) and RFC2218 (October 1997, A Common Schema for the Internet White Pages Service) explore why and how to create an Internet white pages service.

RFC2307 (March 1998, An Approach for Using LDAP as a Network Information Service) suggests that an LDAP directory can unify the lookup of a number of different kinds of intranet entities, including users and groups, email aliases, IP services, and shared filesystems.

RFC2538 (March 1999, Storing Certificates in the Domain Name System (DNS)) suggests that the DNS can support key-management activities. Say its authors, “Cryptographic public keys are frequently published and their authenticity demonstrated by certificates. A CERT resource record (RR) is defined so that such certificates and related certificate revocation lists can be stored in the Domain Name System (DNS).” RFC2587 (June 1999, Internet X.509 Public Key Infrastructure - LDAPv2 Schema) explores the same idea but for LDAP rather than DNS.

RFC2425 (September 1998, A MIME Content-Type for Directory Information) defines the text/directory MIME type as a container for directory information. No specific directory implementation is assumed. Examples show how to encapsulate directory entries in both LDIF and vCard formats. RFC2426 (September 1998, vCard MIME Directory Profile) defines the “vCard profile,” which captures the information that typically appears on a business card. See the Internet Mail Consortium (http://www/pdi.org/) for more on vCard.