LDAP Paged Results
You can specify the size of a page that the ADC expects to receive as the result of an LDAP search. Set the Windows Server entries per page value for AD and Exchange Server entries per page value for the DS to reflect the desired page size. These settings are part of the CA's properties. You need to configure both settings on a two-way CA; only the appropriate setting is available for a one-way CA.
Paging groups together objects that are being synchronized, to improve performance. Large page sizes have more entries per page and therefore result in fewer requests to AD and the DS. However, large pages require more memory.
The default page-size setting for the ADC is 20 entries per page. You must configure the corresponding AD and DS to return pages with a compatible number of entries to the ADC's setting. If you use the ADC's default setting of 20 entries per page, AD and the DS can return pages with more than 20 entries; however, configuring AD and the DS to return pages with fewer than 20 entries results in replication errors.
The Exchange 5.5 LDAP service's default configuration is to return 100 entries per page. To modify this setting, change the Maximum number of search results returned value on the LDAP Properties dialog box's Search tab, as Figure 2 shows.
By default, Win2K AD servers return 1000 entries in an LDAP page; Windows 2003 AD servers return 1500 entries. You can use the Ntdsutil utility to modify the AD LDAP page size. Run the utility and enter the commands that Listing 1 shows. (For more information about Ntdsutil, see the Windows IT Pro article "Using Ntdsutil to Defrag AD," June 2003, Instant-Doc ID 38945.) This script updates the lDAPAdminLimits attribute on AD's default query policy. You can use ADSI Edit to see the lDAPAdminLimits attribute's value (under Configuration Naming Context/Services/WindowsNT/Directory Service/Query-Policies), as Figure 3 shows.
In most cases, the default LDAP page settings are sufficient and you don't need to modify them. If you decide to make changes, consult Microsoft Product Support Services (PSS) or other experts. Without modifying the source directory systems, you can configure the ADC to process 100 entries from the Exchange 5.5 LDAP service and 1000 entries from AD to gain a small performance improvement. But even this change is valuable only if you expect significant data volumes during synchronization.
Fine-Tune at Will
The ADC provides solid functionality to help Exchange 5.5 environments work seamlessly with Exchange 2003 environments. The ADC's default configuration is adequate for most situations, but you can fine-tune the ADC to improve synchronization in your environment.
Kieran McCorry (kieran.mccorry@ hp.com), based in Ireland, is a principal consultant in HP's Advanced Technology Group and a Microsoft Exchange MVP. His most recent book is Microsoft Exchange Server 2003 Deployment and Migration (Digital Press).