Active Directory Sites

Active Directory uses sites to map a organizations physical network.A site is a collection of well-connected subnets.A simple method of transfering updates and other changes to Active Directory is to let all servers communicate directly with each other,this is not ideal because it places high requirements on network bandwidth and is ineffective in network environments that uses slower WAN links.

By using sites Active Directory can automatically determine the best method for performing replicaton.Sites take into account the organizations network infrastructure and Active Directory uses sites to determine the most efficent method for synchronizing information between domain controllers.

Whenever a change is made it is given an update sequence number,the domain controller can then propagate the changes to the other domain controllers based on the replication settings. Windows Server 2016 uses a feature called linked value replication that is only active when the domain is in Windows Server 2003,2008,2008 R2,2012,2012 R2 or 2016 domain fuctional level.

Configuring Replication

When managing replication traffic between sites there are two types of sychronization Intrasite and Intersite.In Intrasite replication one domain controller contacts the others in the same site when a change is made using Remote Procedure Call protocol.Intersite replication is optimized for low-bandwidth situations and connections that have less reliability.You can use two different protocols to transfer information,the RPC over IP or Simple Mail Transfer Protocol. You almost always use IP site links because they are encrypted and authenticated.

Implementing Sites and Subnets

The basic objects used for managing replication is:

Subnets:A partition of a network.

Sites: A Active Directory site is a logical object that contain servers and other objects related to replication.

Site links:A site link is created to define the types of connections that are available between the components of a site.

Creating Sites and Subnets

To create a site open the Active Directory Sites and Services Tool from Administrative Tools.Then expand the Sites folder Right-click the Default-First-Site-Name item and choose rename.Create a new site by right-clicking the Sites object and select New Site. After you have created sites to map your network topology you then need to define the subnets that define site boundaries. Open the Active Directory Sites and Services Tool from Administrative Tools and expand the Sites folder.Right-click Subnets folder and select New Subnet. After you have provided information about sites,subnets,site-links and site-link bridges the Knowledge-Consistency Checker creates the replication topology. The default replication interval is 180 minutes which you can configure.

Monitoring and Troubleshooting Active Directory Replication

For the most the part replication between domain controllers is automatic.However you still need to monitor the performance of the replication because incorrect configurations can sometimes prevent the syncronization of information between domain controllers.

To do this you can use the System Monitor Administration Tool.You can take several steps to troubleshooting the replication:

1.Verify Network Connectivity

2.Verify Router and Firewall Configurations

3.Check the Event Logs if a replication configuration error occurs information is written to the Directory Service and File Replication Services event logs.

4.Verify that the Information is Syncronized

5.Verify Authentication Scenarios

6.Check Replication Topology.The Active Directory Sites and Services Tool allows you to verify the replication topology.To do this right-click the NTDS Settings within a Server object and choose All Tasks and then check Replication,or you can use the command-line utility Repadmin.