16.8 Configuring for Superior Referrals

Often, larger deployments need a directory tree that uses LDAP server software from different vendors. Such a tree is a global federated tree. LDAP Services for eDirectory 8.8 has the capability to return referrals to a superior DSA in a federated tree.

16.8.1 Scenario: Superior Referrals in a Federated Tree

Luc is responsible for networks at Digital Airlines. An OpenLDAP server is being used to master the root of a directory tree at Digital Airlines (from the tree root down to O=Digital Airlines). An organization (OU=Sales) is mastered by an eDirectory server, and another organization (OU=Dev) is held on an iPlanet server.

The following figure illustrates this tree:

Multi-vendor LDAP data

eDirectory masters only the data within the partition for OU=Sales. The data in the other areas are mastered on non-eDirectory DSAs. Luc configures LDAP Services to return superior referrals whenever an operation is rooted at O=Digital Airlines or above, or anywhere under O=Digital Airlines that is not part of the OU=Sales hierarchy.

An operation is sent to the eDirectory LDAP server with a base DN of OU=Dev,O=Digital Airlines,C=US. A referral is returned pointing to the servers holding that entry or to servers that have knowledge of the servers holding that entry.

Likewise, a subtree search rooted at O=Digital Airlines,C=US results in a referral to the root DSA. The root DSA in turn returns referrals to the DSAs mastering OU=Sales and OU=Dev.

So that the eDirectory server can participate in this tree, LDAP Services allows eDirectory to hold the hierarchical data above it in a partition marked “nonauthoritative.” The objects in the nonauthoritative area consist only of those entries needed to build the correct DN hierarchy. These entries are analogous to X.500 “Glue” entries.

In this scenario, the Root, C=US, and O=Digital Airlines objects are held on the eDirectory server in a nonauthoritative area.

eDirectory allows knowledge information (referral data) to be placed within nonauthoritative areas.This information is used to return referrals to the LDAP client.

When an LDAP operation takes place in a nonauthoritative area of the eDirectory tree, the LDAP server locates the correct reference data and returns a referral to the client.

16.8.2 Creating a Nonauthoritative Area

The following figure illustrates the actual data held on the eDirectory server in the federated tree shown in Scenario: Superior Referrals in a Federated Tree.

Data held on the eDirectory server

Notice that entries are placed above OU=Sales, even though these entries are mastered by another DSA. This placement is necessary to provide the proper DNs for the entries mastered by the eDirectory server.

To create a nonauthoritative area:

  1. Segregate the nonauthoritative data from the authoritative data.

    Create a partition boundary at the top of the authoritative area. An eDirectory server considers itself authoritative for all data that it holds unless otherwise specified.

  2. Mark the root partition as nonauthoritative.

    1. Add the authoritative attribute to the rootmost entry in the partition.

    2. Populate the authoritative attribute with a value of zero.

  3. Draw a boundary at the bottom of the nonauthoritative area.

    Create partition roots at the areas of the subtree that this server is to be authoritative for. For example, in the figure above, a partition root exists at the OU=Sales entry. The new partitions won't have the authoritative attribute set to zero. Therefore, the server will be authoritative for the partitions.

  4. Refresh the LDAP server.

    The LDAP server caches the authoritative and nonauthoritative area boundaries whenever its configuration is refreshed. If you don't manually refresh the server configuration, the server will automatically refresh itself on a 30-minute background task.

    Multiple partitions can be stacked in a chain of nonauthoritative areas. However, LDAP Services for eDirectory 8.8 requires that all nonauthoritative partitions must be contiguous and held in local replicas.

16.8.3 Specifying Reference Data

When the LDAP server finds that an operation is taking place in a nonauthoritative area, it looks for information it can use to return a referral to the client. This referral information might be at one of the following:

  • Located on any or all of the entries in the nonauthoritative area

  • Specified as a default referral on the LDAP server or LDAP Group object that holds the configuration data for the server

Referral information held on entries in the nonauthoritative area is an Immediate Superior Reference. Such referral information consists of a multi-valued ref attribute. For a description of this attribute, see RFC 3296.

Referral information held in the Default Referral configuration setting is a Superior Reference and is single-valued. See immSupr and supr DSE types in X.501.

Reference data is held in the form of an LDAP URL, but only specifies the host and (optionally) the port of the DSA being referred to. The following example illustrates this reference data:


The LDAP server looks at the base DN for the operation (or if not found, the matched DN). If the base DN contains reference information, the LDAP server returns that information as a referral.

If no reference information is found, the LDAP server traverses the tree upwards, looking for reference information. If no reference information is found after exhausting all entries, the LDAP server returns the superior reference. This reference is held in the default referral setting on the LDAP Group or LDAP Server object.

Adding an Immediate Superior Reference

You can add an auxiliary object class called immediateSuperiorReference to an entry in the nonauthoritative area. This auxiliary class adds a ref attribute, which is populated with one or more LDAP URLs. Each URL points to a DSA’s host name and (optionally) port.

Adding a Superior Reference

Historically, the LDAP Group object has had an ldapReferral attribute. This attribute held a default reference that was used for various failover situations when returning referrals to other eDirectory servers in an eDirectory tree. In LDAP Services for eDirectory 8.8, this attribute is used to hold a single default referral to a superior DSA in a federated tree.

Additionally, the ldapReferral attribute has been added to the LDAP server object. If the ldapReferral attribute contains a value on the LDAP server object, that setting overrides the value held in the same attribute on the LDAP Group object. This behavior allows you to configure all LDAP servers participating in a group to have a particular default referral, while one or two servers override that value with a different default referral.

The value on the ldapReferral attribute is an LDAP URL. The URL holds the host and optional port of the DSA being referred to.

16.8.4 Updating Reference Information through LDAP

If you followed the steps above, in order, and used LDAP to perform the tasks, you were likely unable to add an immediate superior reference. This is because the root partition had already been marked nonauthoritative, so LDAP sends referrals for any operation acting on data within that partition.

To update or interrogate information in a nonauthoritative area, the ManageDsaIT control must accompany the LDAP request. For information on this control, see RFC 3296. This control effectively causes the LDAP server to treat the entire nonauthoritative area as though it is authoritative.

NOTE:The superior reference feature is only available through LDAP. Other protocols (for example, NDAP) are not affected by the presence of the authoritative attribute. Therefore, the use of NetIQ iManager to interrogate and update data in the nonauthoritative area is unhindered.

16.8.5 Affected Operations

Nonauthoritative areas and superior referrals affect the following LDAP operations:

  • Search and Compare

  • Modify and Add

    DN-syntax attribute values are not checked. Therefore, a group member attribute can contain DNs that point to entries in a nonauthoritative area.

  • Delete

  • Rename (moddn)

  • Move (moddn)

    If the parent DN falls within a nonauthoritative area, an error affectsMultipleDSAs should be returned.

  • Extended

16.8.6 Discovering Support for Superior References

Support for superior referrals is available only in LDAP Services for eDirectory 8.7 and later. To discover whether an eDirectory server supports this functionality, you can read the supportedFeatures attribute on the root DSE. If the supportedFeatures attribute lists the OID 2.16.840.1.113719., these features are available. Additional discovery-related changes to the root DSE object include the following:

  • namingContexts

    This attribute only lists the partition roots held on the local DSA that the server is authoritative for. No nonauthoritative partition roots are listed.

  • altServer

    This attribute won't list other eDirectory servers that share only nonauthoritative partitions with the local server.

  • superiorReference

    This attribute advertises the superior referral for the DSA. This value is administered by updating the ldapReferral attribute on the LDAP Server or LDAP Group object.