LDAP System Administration

What Is the dc Attribute?

Returning to our discussion of the topmost entry in Figure 2-1, we can now explain the meaning of the domain object class and the dc attribute. Here is the original LDIF listing for the entry:

# LDIF listing for the entry dn: dc=plainjoe,dc=org
dn: dc=plainjoe,dc=org
objectclass: domain
dc: plainjoe

The original recommendation for dividing the X.500 namespace was based on geographic and national regions. You frequently see this convention in LDAP directories as well, given the heritage that LDAP shares with X.500. For example, under X.500, the distinguished name for a directory server in the plainjoe.org domain might be:

dn: o=plainjoe,l=AL,c=US

Here, the o attribute is the organizationName, the l attribute is the locality of the organization, and the c attribute represents the country in which the organization exists. However, there is no central means of registering such names, and therefore no general way to refer to the naming context of a directory server. RFC 2247 introduced a system by which LDAP directory naming contexts can be piggybacked on top of an organization’s existing DNS infrastructure. Because DNS domain names are guaranteed to be unique across the Internet and can be located easily, mapping an organization’s domain name to an LDAP DN provides a simple way of determining the base suffix served by a directory and ensures that the naming context will be globally unique.

Note

A directory’s naming context is the DN of its topmost entry. The ...