However, ACI filters can be difficult to manage. Decide which method of access control is best suited to the directory: organizational branching in the directory tree hierarchy, ACI filters, or a combination of the two.

4.2.3 Naming Entries

After designing the hierarchy of the directory tree, decide which attributes to use when naming the entries within the structure. Generally, names are created by choosing one or more of the attribute values to form a relative distinguished name (RDN). The RDN is a single component within the DN. This is the very first component shown, so the attribute used for that component is the naming attribute, because it sets the unique name for the entry. The attributes to use depends on the type of entry being named.

The entry names should adhere to the following rules:

•The attribute selected for naming should be unlikely to change.

•The name must be unique across the directory.

A unique name ensures that a DN can refer to at most one entry in the directory.

When creating entries, define the RDN within the entry. By defining at least the RDN within the entry, the entry can be located more easily. This is because searches are not performed against the actual DN but rather the attribute values stored in the entry itself.

Attribute names have a meaning, so try to use the attribute name that matches the type of entry it represents. For example, do not use l to represent an organization, or c to represent an organizational unit.

•“Naming person entries”

•“Naming group entries”

•“Naming organization entries”

•“Naming other kinds of entries”

4.2.3.1Naming person entries

The person entry's name, the DN, must be unique. Traditionally, distinguished names use the commonName, or cn, attribute to name their person entries. That is, an entry for a person named Babs Jensen might have the distinguished name of cn=Babs Jensen, dc=example,dc=com.

While using the common name makes it easier to assocaited the person with the entry, it might not be unique enough to exclude people with identical names. This quickly leads to a problem known as DN name collisions, multiple entries with the same distinguished name.

Avoid common name collisions by adding a unique identifier to the common name, such as cn=Babs Jensen+employeeNumber=23,dc=example,dc=com.

However, this can lead to awkward common names for large directories and can be difficult to maintain.

A better method is to identify the person entries with some attribute other than cn. Consider using one of the following attributes:

•uid

Use the uid attribute to specify some unique value of the person. Possibilities include a user login ID or an employee number. A subscriber in a hosting environment should be identified by the uid attribute.

•mail

Use the mail attribute to contain the value for the person's email address. This option can lead to awkward DNs that include duplicate attribute values (for example: mail=bjensen@example.com, dc=example, dc=com), so use this option only if there is not some other unique value to use with the uid attribute. For example, use the mail

46 Designing the directory tree