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Exchange 2000 Server is dependent on the Microsoft Windows 2000 Active Directory for both user and configuration information. Exchange 2000 predominantly uses Lightweight Directory Access Protocol (LDAP) to communicate to the domain controller and global catalog servers for this information. Exchange 2000 uses Active Directory very efficiently, but for many server and user actions a LDAP directory lookup is required.
When there are numerous Exchange 2000 servers in a Windows 2000 site, a very large LDAP load may be put on the Active Directory servers. By default, Active Directory is configured to have a MaxActiveQueries value of 20 (LDAP queries). This setting is the maximum number of pending LDAP queries that Active Directory can process.
If this limit is reached, Active Directory returns an error message "LDAP_ADMIN_LIMIT_EXCEEDED" and does not process further LDAP queries. A MaxActiveQueries value of 20 is generally sufficient for most Active Directory servers, but you may need to increase this value if you are running domain controllers on servers that have six or eight processors and you receive this error message.
You can increase the MaxActiveQueries value by using the Windows 2000 Ntdsutil.exe tool.
If you increase this setting, a little more memory is used in the Lsass.exe process in Active Directory, so do not increase this value any higher than necessary. The procedure to change this value is outlined in the following example:
Active Directory picks up this change without restarting. In the preceding example, Active Directory processes no more than 40 LDAP queries at a time.
c:\>ntdsutil.exe ntdsutil: Ldap policies ldap policy: connections server connections: Connect to server DCServer1 Binding to DCServer1 ... Connected to DCServer1 using credentials of locally logged on user server connections: q ldap policy: Show Values Policy Current(New) MaxPoolThreads 8 MaxDatagramRecv 1024 MaxReceiveBuffer 10485760 InitRecvTimeout 120 MaxConnections 5000 MaxConnIdleTime 900 MaxActiveQueries 20 MaxPageSize 1000 MaxQueryDuration 120 MaxTempTableSize 10000 MaxResultSetSize 262144 MaxNotificationPerConn 5 ldap policy: set MaxActiveQueries to 40 ldap policy: Commit Changes ldap policy: Show Values Policy Current(New) MaxPoolThreads 8 MaxDatagramRecv 1024 MaxReceiveBuffer 10485760 InitRecvTimeout 120 MaxConnections 5000 MaxConnIdleTime 900 MaxActiveQueries 40 MaxPageSize 1000 MaxQueryDuration 120 MaxTempTableSize 10000 MaxResultSetSize 262144 MaxNotificationPerConn 5 ldap policy: q ntdsutil: q Disconnecting from DCServer1
NOTE: This setting is global to all Active Directory servers in the forest. If you change this value on one Active Directory server, all the other domain controllers in the forest pick up the change as well.