Configuring and Troubleshooting Active Directory Replication

An Overview of Active Directory Replication

Active Directory is a distributed multimaster replicated database. All domain controllers host a full replica of the domain information for its own domain. Domain controllers in Windows 2000 and Windows Server 2003 environments hold a read/write copy of the Active Directory database. In these environments, changes can be made to the Active Directory database on any domain controller within the Active Directory environment. Replication is the process that ensures that changes made to a replica on one domain controller are transferred to replicas on the remainder of the domain controllers. When an object in Active Directory is created, deleted, moved, or changed; Active Directory replication is triggered.

In Windows 2000 and Windows Server 2003 environments, the types of Active Directory replication that can be defined are:

The information replicated in Active Directory is summarized below:

You can use the Active Directory Sites and Services console to configure intersite replication. Configuring intersite replication typically involves:

How to rename the Default-First-Site-Name Site (first site object)

You have to rename the default site object to something that has meaning in your organization. To do this,

  1. Open the Active Directory Sites and Services console
  2. Right-click Default-First-Site-Name, and select Rename from the shortcut menu.
  3. Proceed to set a meaningful name for the site.

How to create a new site object

  1. Open the Active Directory Sites and Services console
  2. Right-click the Sites folder and select New Site from the shortcut menu.
  3. When The New Object - Site dialog box opens, enter a name for the site in the Name box.
  4. You can accept DefaultIPSiteLink in the Link Name box.
  5. Click OK.

How to create a new subnet object

  1. Open the Active Directory Sites and Services console
  2. Right-click the Subnets folder, and select New Subnet from the shortcut menu
  3. When The New Object – Subnet dialog box opens, in the first section of the dialog box, specify the subnet address and the number of bits in the subnet mask.
  4. In the Select a site object for this subnet section, specify the site object to which this particular subnet is associated with.
  5. Click OK.

How to create a site link

When you create a site link you can specify the transport protocol for replicating data over site links as either IP or SMTP.

To create a site link,

  1. Open the Active Directory Sites and Services console
  2. Open the Sites folder, and then open the Inter-Site Transports folder
  3. Right-click either the IP folder or the SMTP folder, and choose New Site Link from the shortcut menu.
  4. The New Object–Site Link dialog box opens
  5. In the Name field, enter a name for the new site link.
  6. In the Sites Not In This Site Link box, select the sites to connect. Click Add
  7. Click OK.

How to configure site link attributes or properties

Configuring site link attributes involves specifying site link costs, the site link replication frequency, and setting site link replication availability. When you set the site link cost, you are basically defining the cost of the network connection proportionate to the speed of the link. Lower costs are utilized for fast links, while higher costs are associated with slower links. The site link replication frequency can be a number ranging from 15 minutes to 10,080 minutes. Setting site link replication availability involves specifying when a site link is available for replication.

To configure site link attributes,

  1. Open the Active Directory Sites and Services console
  2. Open the Sites folder, and then open the Inter-Site Transports folder.
  3. Open the IP folder or SMTP folder which contains the site link that you want to configure site link attributes for.
  4. Right-click the particular site link and then select Properties from the shortcut menu.
  5. In the Description box in the General tab of the Properties dialog box for the site, you can enter a description for the site link.
  6. In the Cost box, you can change the default cost for the site link, and assign a cost to the link. The default cost setting is 100.
  7. In the Replicate Every box, you can change the default replication interval. This is basically the number of minutes between replications. The default setting is 180 minutes. The shortest replication interval that can be set is 15 minutes, and the longest interval that can be specified is 10,080 minutes.
  8. Click the Change Schedule button to configure when the site link is available for replication.
  9. When the Schedule dialog box for the site link opens, you can set when the site link is available for replication, or when it is not available for replication.
  10. Click OK to save configuration changes you made in the Schedule dialog box.
  11. Click OK to save changes in the Properties dialog box of the site.

How to configure replication to disregard/ignore schedules

  1. Open the Active Directory Sites and Services console
  2. Open the Sites folder, and then open the Inter-Site Transports folder.
  3. Right-click the IP folder or SMTP folder and choose Properties from the shortcut menu.
  4. When the Properties dialog box of the folder which you selected opens, click the Ignore Schedules checkbox.
  5. Click OK.

How to add a site to an existing site link

  1. Open the Active Directory Sites and Services console
  2. Open the Sites folder, and then open the Inter-Site Transports folder.
  3. Open the IP folder or SMTP folder that contains the site link to which the site should be added.
  4. Right-click the particular site link and then select Properties from the shortcut menu.
  5. Use the Sites Not In This Site Link box to select the site that should be added to the site link. Click Add.
  6. Click OK.

How to rename an existing site link

  1. Open the Active Directory Sites and Services console
  2. Open the Sites folder, and then open the Inter-Site Transports folder.
  3. Open the IP folder or SMTP folder that contains the site link that you want to rename.
  4. Right-click the particular site link and then select Rename from the shortcut menu.
  5. Proceed to set a new name for the site link.

How to designate a preferred bridgehead server (BS)

The Knowledge Consistency Checker (KCC) could possibly not designate a bridgehead server that is the most optimal domain controller in a site. In cases like this, to improve performance, you can manually designate a preferred bridgehead server(s).
To designate a preferred BS,

  1. Open the Active Directory Sites and Services console
  2. In the console tree, expand the Sites folder, expand the site in which you want to create the bridgehead server, and then expand the Servers folder.
  3. Right-click on the particular server, and select Properties from the shortcut menu.
  4. When the Properties dialog box of the server opens, in the Transports available for inter-site transfer section, select the protocol for which the server is to be a bridgehead server. Click Add.
  5. Click OK.

How to disable transitive site links, or automatic bridging

Because site link transitivity is enabled by default, you would typically need to disable it if you want to create site link bridges.

  1. Open the Active Directory Sites and Services console
  2. Open the Sites folder, and then open the Inter-Site Transports folder.
  3. Right-click either the IP folder or SMTP folder and choose Properties from the shortcut menu.
  4. On the General tab, uncheck the Bridge All Site Links checkbox to disable site link transitivity.
  5. Click OK.

How to create a site link bridge

  1. Open the Active Directory Sites and Services console
  2. Open the Sites folder, and then open the Inter-Site Transports folder.
  3. Right-click either the IP folder or SMTP folder and choose New Site Link Bridge from the shortcut menu.
  4. The New Object–Site Link Bridge dialog box opens.
  5. Enter a name for the new site link bridge in the Name field.
  6. Use the Site links not in this bridge box to select two or more sites to connect. Click Add
  7. Click OK

How to manually create and configure a connection object

Connection objects in Active Directory are automatically created by the KCC. You can however manually create connection objects to customize the topology of the network, or to decrease the number of hops from one domain controller to another particular domain controller. When connection objects are created by the KCC, they are automatically removed by the KCC when the replication topology changes. Connection objects that are manually created are not removed when the replication topology changes. You have to manually remove these connection objects.

To manually create and configure connection objects,

  1. Open the Active Directory Sites and Services console
  2. In the console tree, expand the Sites folder, expand the site in which you want to create the connection object, and then expand the Servers folder.
  3. Select the particular server that you want to enable the connection for.
  4. Right-click NTDS Settings and select New Active Directory Connection from the shortcut menu.
  5. When the Find Domain Controllers dialog box opens, choose the domain controller. Click OK
  6. When the New Object–Connection dialog box opens, enter a name for the connection object. Click OK
  7. Proceed to right-click the connection that you have just created in the details pane and select Properties from the shortcut menu.
  8. When the Properties dialog box of the connection object opens, in the Description field, provide a description for the new connection object.
  9. In the Transport drop down list, verify that RPC is specified as the transport protocol.
  10. If you want to modify the default schedule for intrasite replication, click the Change Schedule button.
  11. When the Schedule dialog box for the connection object opens, set the appropriate replication frequency and Click OK.
  12. Click OK to save changes made in the Properties dialog box of the connection object.

How to manually force immediate replication

  1. Open the Active Directory Sites and Services console
  2. In the console tree, expand the Sites folder, expand the site that Active Directory has to replicate to and then expand the name of the server to use for replication.
  3. Click NTDS Settings to display the inbound connection objects of the server in the right pane.
  4. Right-click the server that you want to replicate from and click Replicate Now from the shortcut menu.

Troubleshooting Active Directory Replication

Although domain controllers generally automatically manage the replication process, there are instances when incorrect configuration settings or troublesome network connections can prevent Active Directory information from being replicated between domain controllers. There are quite a few mechanisms that can be used to monitor and troubleshoot the Active Directory replication process.
The tools available are:

A few common methods that you can use to monitor or troubleshoot Active Directory replication are summarized below:

There may be instances when Active Directory replication is quite slow. A few methods of correcting this problem are summarized below:

How to use Active Directory Replication Monitor to monitor/troubleshoot replication

Replication Monitor (Replmon) is a graphical management tool included in the Windows Support Tools. In order to open and use Replmon, it must be installed on a computer running. The computer can be a domain controller, member server, member workstation or stand-alone computer. Replication Monitor can be used to perform the following activities:

The information displayed in the main Replication Monitor window is listed below:

Once you have specified a domain controller for monitoring, you can set view options to suit your needs. To specify view options, open Replication Monitor, and select Options from the View menu. The options that can be selected on the General tab are:

The Replmon replica synchronization options that can be selected are listed below. These options can be configured by right-clicking a monitored server object, and then selecting Synchronize Each Directory Partition with All Servers. The synchronization options that you can select are:

How to start Replication Monitor

Remember that you first have to install Replication Monitor.

  1. Click Start, Windows Support Tools, Command Prompt and enter replmon.exe.
  2. When the Replication Monitor opens, in the console tree, right-click Monitored Servers and select Add Monitored Server from the shortcut menu.
  3. The Add Monitored Server Wizard now starts
  4. Select the Add The Server Explicitly By Name option. Click Next.
  5. In the Add Server To Monitor page, use the Enter The Name Of The Server To Monitor Explicitly box to specify the name of the server that should be monitored.
  6. Click Finish
  7. The server that you specified for monitoring is now displayed in the console tree.

How to synchronize the Active Directory directory partition

Domain controllers that are indicated for a directory partition are regarded as source servers. Source servers can be a Direct Replication Partner, a Transitive Replication Partner or a Bridge Head Connection.
To synchronize the directory partition,

  1. Open Replication Monitor
  2. Right-click the direct replication partner and then choose Synchronize Replica from the shortcut menu.
  3. Replication Monitor now starts the replication process and reports on the status of replication as well.

How to use the Replication Diagnostics Tool to monitor/troubleshoot Active Directory replication

The Replication Diagnostics Tool (Repadmin) is a command-line interface that can be quite useful when troubleshooting Active Directory replication. Through Repadmin, you can perform the following:

The online help shows the syntax for options and switches of Repadmin. Run repadmin /? for online help. If you want to determine the status of the KCC for replication, run repadmin/kcc. If you want to determine what the replication result was for the last replication process performed, run repadmin/showreps. If you are running Windows Server 2003, Repadmin offers a few additional functions that can be performed. To view these, run repadmin/experthelp.

How to configure Active Directory event logging

You can also configure Active Directory event logging. A few key events that can be specified for event logging are listed below:

You can set one of the following logging levels for an event:

How to enable Active Directory event logging

  1. Click Start, Run and enter regedit in the Run dialog box. Click OK
  2. This opens the Registry Editor.
  3. Click the HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\NTDS\Diagnostics registry key.
  4. The entries that are displayed in the right pane are the types of events that can be logged. The default logging level for each entry is 0 – None.
  5. Open the entry for each type of event that you want to log by double-clicking it.
  6. In the Value data box of each entry, enter the logging level.
  7. Click OK.

How to use Dsastat.exe tomonitor/troubleshoot Active Directory replication

You can use Dsastat.exe to compare the attributes of replicated objects and to determine differences between directory partitions hosted by domain controllers. Dsastat.exe uses statistics such as objects per server, and megabytes per server to determine what the differences are in Active Directory information between domain controllers.

The syntax for Dsastat is:

dsastat [/loglevel:option] [/output:option] [/s:servername[portnumber][;servername[portnumber];...]] [/t:option] [/sort:option] [/p:entrynumber] [/scope:option] [/b:searchpath] [/filter:ldapfilter] [/gcattrs:option[;option;...]] [/u:username] [/pwd:password] [/d:domain]



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