Configuring Inter-site Replication
After you have a plan in place that defines your sites, IP subnets, site links, costs, and bridgeheads, you can proceed to create the objects in Active Directory. Here is the general course of action:
After completing this work, the KCC should handle any changes you make to the distribution of domain controllers and Global Catalog servers in the network with no further intervention.
Rename the Default-First-Site-Name Site
The name for the first site is a little long and clumsy for most uses. The steps to rename it are listed in Procedure 7.4.
Procedure 7.4 Renaming the Default-First-Site-Name Object
Open the AD Sites and Services console.
Right-click the Default-First-Site-Name object and select RENAME from the flyout menu. The object name gets a bounding box and a blue background.
Change the name to the name of the site in your site plan and press Enter. The example shows a new name of Phoenix.
Leave the console open. You need it to perform the next steps.
The name change is registered with DNS automatically. Verify using the DNS console that the name change took effect. This ensures that the site references used by the Active Directory clients are correct. If the DNS server is offline when you change the name, or if you lose network connection while the change is replicating, the new site name will be registered as soon as connection to DNS is re-established. You may need to delete the old site name manually from the zone table.
Create New Sites
After you rename the first site, create site objects for the remaining sites in your plan. Do this using the AD Sites and Services console as shown in Procedure 7.5.
Procedure 7.5 Creating a New Site Object
Right-click the Sites object and select NEW SITE from the flyout menu. The New Object Ц (Site) window appears (see Figure 7.10).
Figure 7.10. New Object Ч (Site) window.
Under Name, enter the name of the site. The example uses a site name of Houston.
Under Link Name, highlight DefaultIPSiteLink. This is only a placeholder. You'll be creating specific links a little later.
Click OK to create the Site object.
When you create the Site object, the system automatically creates a Server container and two Settings objects, Licensing Site Settings and NTDS Site Settings. The system also adds several SRV records to DNS that point at the new domain controller. These records are grouped under the _msdcs and _sites headings.
Create IP Subnets
Active Directory uses subnets to differentiate between sites. Create Subnet objects for each subnet in your network as shown in Procedure 7.6.
Procedure 7.6 Creating a Subnet Object
Right-click the Subnets object and select NEW SUBNET from the flyout menu. The New Object Ц (Subnet) window appears (see Figure 7.11).
Figure 7.11. New Object Ч (Subnet) window showing subnet for the Phoenix site.
Under Name, enter the subnet address and the number of bits in the subnet mask. The example uses a private 10-space network, 10.1.1.0, with a 24-bit mask corresponding to 255.255.255.0.
Select a Site object to associate with the Subnet object. The example uses the Phoenix site. If you have more than one subnet in a Site, you can create multiple Subnet objects and associate them with the same site.
Click OK to create the subnet object and return to the main console window.
Use the same procedure to create Subnet objects for all the subnets in your network.
Create Site Links
You are now ready to create and configure the necessary Site Link objects to describe your network infrastructure. Follow the steps in Procedure 7.7.
Procedure 7.7 Creating and Configuring Site Link Objects
Expand the tree to find the IP object under Sites | Inter-Site Transports.
Right-click the IP object and select NEW SITE LINK from the flyout menu. The New Object Ц (Site Link) window appears (see Figure 7.12).
Figure 7.12. New Object Ч (Site Link) window.
Under Name, enter a name for the Site Link object.
Select two sites and click Add to put them in the Sites In This Link list. You must have at least two sites associated with a Site Link.
Click OK to create the object.
Open the Properties window for the new Site Link object (see Figure 7.13).
Figure 7.13. Site Link Properties for the Phoenix to Houston link showing description, cost, and interval.
Enter a Description for the link. You might want to include the type of connection, the bandwidth, and any helpful information that helps you isolate problems should you have trouble with the link.
Assign a Cost to the link. This is the highest-speed link in the example network, so it gets a cost of 1. For the 512K links to the branch offices, assign a cost of 20. For the emergency ISDN line, assign a cost of 100. Keep the options to a minimum. The KCC uses these numbers to build a spanning tree map. If you use too many values, you'll confuse matters rather than help them.
Shorten the default Replication interval unless the link is especially slow or heavily subscribed. The shortest interval that the system accepts is 15 minutes. If you enter a shorter interval, the change is accepted, but the interval is set to 15.
Click Change Schedule. The Schedule window opens for the link (see Figure 7.14).
Figure 7.14. Schedule window for the Phoenix to Houston Site Link showing that replication is available 7x24.
If the connection is up at certain times, clear the blue for the intervals where it is not available. Use this option if you have a slow link that experiences peak traffic at certain times and you don't want to add replication traffic to the mix. When you play games with replication intervals, keep in mind that you're affecting latency.
Click OK to save the change and return to the Properties window.
Click OK to save the changes and return to the console.
Close the console.
Now create Site Link objects for the remaining connections between sites.
Designating Bridgehead Servers
The KCC may select a bridgehead that is not the most capable domain controller in a site. Or it may select a bridgehead that is not a Global Catalog server, which would require the system to create additional connections to handle GC replication between sites.
You can reduce the complexity of inter-site replication and improve performance by selecting preferred bridgehead servers. It is important to designate multiple preferred bridgeheads so that the failure of a single server does not cause a failure of inter-site replication. Procedure 7.8 designates a Bridgehead server.
Procedure 7.8 Designating a Bridgehead Server
Open the AD Sites and Services console.
Expand the tree to show the Server object representing the domain controller you want to use for a bridgehead server.
Right-click the Server object and select PROPERTIES from the flyout menu. The Properties window opens (see Figure 7.15).
Figure 7.15. Properties window for server showing transports that have been added to the bridgehead list.
Select the IP transport and click Add to move it to the bridgehead side of the window.
Click OK to save the change.
The Computer field indicates the Computer object associated with the Server object used to control replication. The two names should always be the same.
Another common reason for designating specific Bridgehead servers is to configure replication through a firewall. By assigning the servers that handle inter-site replication, you can configure the firewall to pass traffic only from those servers.
You can designate the port used by the bridgehead server. This helps to configure replication through the firewall. This option requires a Registry entry:
Key: HKLM | System | CurrentControlSet | Services | NTDS |
Value: TCP/IP Port
Data: <port number>
Creating Site Link Bridge Objects
You may find after laying out the Site Links and running the system in production a while that the bridgeheads need a bit more information about your network to lay their replication plans effectively. This involves creating specific Site Link Bridge objects to describe preferred routes. Follow the steps in Procedure 7.9 to disable global site link bridging and to build Site Link Bridge objects.
Procedure 7.9 Building a Site Link Bridge Object
Open the AD Sites and Services console.
Right-click the IP object and select PROPERTIES from the flyout menu. The IP Properties window opens (see Figure 7.16).
Figure 7.16. IP Properties window showing the global bridging option.
Deselect the Bridge All Site Links option. This removes the global transitive bridging for site links.
Right-click the IP object and select NEW SITE LINK BRIDGE from the flyout menu. The New Object Ц (Site Link Bridge) window appears (see Figure 7.17).
Figure 7.17. New Object Ч (Site Link Bridge) window.
Select the links you want to define for the preferred route and click Add to put them on the list.
Click OK to save the changes and return to the console. The Site Link Bridge object is added to the list of IP link objects.
Monitor your Event log and Connection object status carefully over the next few hours to see how the KCC reacts to the change.
Only a few more items to take care of, then the job is complete. One of those items is making sure that efficient use is made of the domain controllers when it comes to propagating replication traffic. To do that, we may need Bridgehead servers.