Network connections are represented by site links. By creating site links and configuring their cost, replication frequency, and replication availability, you provide the directory service with information about how to use these connections to replicate directory data. You can improve site link connectivity by linking overlapping existing site links together into site link bridges, or you can bridge all site links and maximize connectivity. You can also designate a server, known as a bridgehead server, to serve as a contact point for the exchange of directory information between sites. This lesson explains how to configure inter-site replication.
After this lesson, you will be able to
Estimated lesson time: 25 minutes
To configure inter-site replication you must complete the following tasks:
You should provide information about site link cost, replication frequency, and replication availability for all site links as part of the process of configuring inter-site replication.
You configure site link cost to assign a value for the cost of each available connection used for inter-site replication. If you have multiple redundant network connections, establish site links for each connection, and then assign costs to these site links that reflect their relative bandwidth. For example, if you have a high-speed T1 line and a dial-up network connection in case the T1 line is unavailable, configure a lower cost for the T1 line and a higher cost for the dial-up network connection. Active Directory always chooses the connection on a per-cost basis, so the cheaper connection is used as long as it is available.
Follow these steps to configure site link cost:
Figure 17.8 Properties dialog box for a site link
Configure site link replication frequency for site links by providing an integer value that tells Active Directory how many minutes it should wait before using a connection to check for replication updates. The replication interval must be at least 15 and no more than 10,080 minutes (equal to one week). A site link must be available for any replication to occur, so if a site link is scheduled as unavailable when the number of minutes between replication updates has passed, no replication will occur.
Follow these steps to configure site link replication frequency:
Configure site link replication availability to determine when a site link will be available for replication. Because SMTP is asynchronous, it typically ignores all schedules. Therefore, do not configure site link replication availability on SMTP site links unless
Follow these steps to configure site link replication availability:
Figure 17.9 Schedule for dialog box for a site link
This following procedure has no effect if you have enabled Ignore Schedules on the Properties dialog box for the inter-site transport.
Follow these steps to ignore schedules for an inter-site transport:
When more than two sites are linked for replication and use the same transport, by default, all the site links are "bridged" in terms of cost, assuming that the site links have common sites. When site links are bridged, they are transitive. That is, all site links for a specific transport implicitly belong to a single site link bridge for that transport. So in the common case of a fully routed IP network (where all sites can communicate with each other via IP), you do not have to configure any site link bridges. If your IP network is not fully routed, you can turn off the transitive site link feature for the IP transport, in which case all IP site links are considered intransitive and you configure site link bridges. A site link bridge is the equivalent of a disjoint network; all site links within the bridge can route transitively, but they do not route outside of the bridge.
Follow these steps to create a site link bridge:
Figure 17.10 New Object-Site Link Bridge dialog box
The following procedure is redundant and has no effect if you have enabled Bridge All Site Links on the Properties dialog box for the inter-site transport.
Follow these steps to bridge all site links for an inter-site transport:
Active Directory automatically creates and deletes connections under normal conditions. Although you can manually add or configure connections or force replication over a particular connection, normally you should allow replication to be automatically optimized based on information you provide to Active Directory Sites And Services about your deployment. Only create connections manually if you are certain the connection is required, and you want the connection to persist until it is manually removed.
Follow these steps to manually configure connections:
Follow these steps to force replication over a connection:
Figure 17.11 Forcing replication over a connection
Ordinarily, all domain controllers are used to exchange information between sites, but you can further control replication behavior by specifying a bridgehead server for inter-site replicated information. Establishing a bridgehead server provides some ranking or criteria for choosing which domain controller should be preferred as the recipient for inter-site replication. This bridgehead server subsequently distributes the directory information via intra-site replication.
Bridgehead servers are the contact point for exchange of directory information between sites. You can specify a preferred bridgehead server if you have a computer with appropriate bandwidth to transmit and receive information. If there is typically a high level of directory information exchange, a computer with more bandwidth can ensure the information exchanges are handled promptly. Matching the demands of your Active Directory deployment with a domain controller with the capacity to handle those demands enables efficient updates of directory information.
You can specify multiple preferred bridgehead servers, but only one will be the active preferred bridgehead server at any time at a single site. If the active preferred bridgehead server fails, Active Directory selects another preferred bridgehead server to be the active preferred bridgehead server from the set you designate. If no active preferred bridgehead server is available and there are no other preferred bridgehead servers available for Active Directory to select, it selects another domain controller in the site to be the preferred bridgehead server. This can be a problem if the domain controller Active Directory selects does not have the bandwidth to efficiently handle the increased requirements posed by being a preferred bridgehead server.
You must specify a preferred bridgehead server if your deployment uses a firewall to protect a site. Establish your firewall proxy server as the preferred bridgehead server, making it the contact point for exchanging information with servers outside the firewall. If you do not do this, directory information may not be successfully exchanged.
Establishing a preferred bridgehead server designates that server as the preeminent server for information exchange over the protocol for which the site link is established. Other domain controllers could still exchange directory information if a need arises, but under normal conditions, the bridgehead server is used as the first choice to receive and send all directory traffic.
Follow these steps to designate a preferred bridgehead server:
In this practice you configure site link cost, replication availability, and replication frequency. You then configure a site link bridge.
Since Active Directory uses cost to determine which connection to use, you need to assign a cost to each site link. In this exercise you assign an arbitrary cost to the Redmond to Chicago site link.
The Active Directory Sites And Services console appears.
The Redmond To Chicago Properties dialog box appears.
In this exercise, you specify how long Active Directory waits before using a this connection to check for replication updates.
In this exercise, you will configure the Redmond To Chicago site link to be available 8:00 am to 9:00 am and 4:00 pm to 5:00 pm, Monday through Friday.
The Schedule For Redmond To Chicago dialog box appears.
In this exercise, you create a bridge between the Redmond To Chicago site link and the DEFAULTIPSITELINK.
The New Object-Site Link Bridge dialog box appears.
In this lesson you learned that you should provide information about site link cost, replication frequency, and replication availability for all site links as part of the process of configuring inter-site replication. Active Directory always chooses the connection on a per-cost basis, so the cheaper connection will be used as long as it is available. You can improve site link connectivity by linking overlapping existing site links together into site link bridges, or you can bridge all site links and maximize connectivity. You also learned that you can designate a domain controller as a bridgehead server to specify which domain controller should be preferred as the recipient for inter-site replication.
In the practice portion of this lesson you configured site link cost, replication availability, and replication frequency. You then configured a site link bridge.