Replication in LDAP

Replication, the key to making a stand-alone directory into a distributed directory, has still not been standardized in LDAP. Version 2 does not even support referrals as part of its core specification. Referrals, which let an LDAP server forward a query to another LDAP server, can be used as a basis for replication.

The University of Michigan designed and implemented an extension to LDAP 2 for referrals, which Netscape, Sun, and others adopted in their LDAP 2 products. A different, standard referral mechanism is part of the core LDAP 3 specification and is supported in Netscape Directory Server 3.0, for instance, where it is used as the basis for master-slave replication.

Interoperability testing on the referral mechanism has been going on informally for some time and formally last June at the Internet Mail Consortium's Dirconnect event. Many other features were tested, as well, in both versions 2 and 3.

LDAPEXT is a new group in the Internet Engineering Task Force (IETF) called to deal with LDAP 3 extensions for replication, access control, server-to-server communication, and C and Java APIs. So far, Netscape has offered its master-slave replication technology. Microsoft and Cisco have offered a multimaster replication scheme.

Novell and IBM have said that they will propose a "mission-critical LDAP" standard, which will include a multimaster replication scheme b ased on Novell Directory Services (NDS) replication technology.

Replication extensions to LDAP 3 may be approved in 1998, says Netscape's Tim Howes, who chairs the committee. We'll be lucky if we see interoperable LDAP-based replication before 1999.