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Site Replication Service

The Active Directory Connector (ADC) provides directory replication between the Exchange Directory and the Windows 2000 AD. The Site Replication Service (SRS) masquerades as a shadow Exchange 5.5 directory server when interacting with other Exchange 5.5 servers in the environment. (See Figure 3.2.) The shadow 5.5 directory server uses mail-based replication over LDAP port 379. Like the ADC, the SRS is needed only in mixed vintage sites, where migration or coexistence is a requirement.

Figure 3.2 The SRS acts as a Shadow Exchange 5.5 directory server to participate in Exchange 5.5 directory replication.


SRS automatically manages the Connection Agreements within the site; no intervention is required.

The SRS is enabled when an Exchange 2000 server turns up in an Exchange 5.5 site. This is the method by which the Exchange 2000 server's SRS can communicate with other 5.5 servers using the intrasite replication mechanism. For most implementations in mixed environments, only a small number of SRS-enabled Exchange 2000 servers exist.

A Configuration Connection Agreement (CCA) is automatically created when an Exchange 2000 server is installed into an Exchange 5.5 site. When it is created, the CCA is always homed against the Exchange 2000 server that is hosting the SRS. This feature provides a certain level of fault tolerance. If the server that the CCA was homed against is upgraded to Exchange 2000 from Exchange 5.5, replication would not be broken. Because the CCA always knows where to find the SRS server, it will maintain the replication link.

Exchange configuration information is not synchronized by the SRS. The ADC and the CCA provide for the transport of configuration information between Exchange 5.5 and Exchange 2000 servers.

When the Exchange 5.5 servers in a mixed environment are upgraded to Exchange 2000, the upgrade process will remove the former Exchange 5.5 server's DSA objects from the Knowledge Consistency Checker (KCC) web. After these Exchange 5.5 servers are upgraded to Exchange 2000, they no longer participate in 5.5 directory replication.

The Site Consistency Checker (SCC) is the consistency checker for the SRS. The SCC preserves intrasite integrity between Exchange 5.5 and Exchange 2000.

SCC (a.k.a. SKCC)— The updated version of the Exchange Server 5.5 Knowledge Consistency Checker (KCC) that works in conjunction with (and is part of) the Exchange Site Replication Service to ensure that knowledge consistency of sites, administration groups, and Active Directory domains is maintained when interoperating between Exchange 2000 and Exchange 5.5.

During the process of upgrading bridgehead servers, the SRS plays an important role. This is because the newly upgraded bridgehead server (from Exchange 5.5 to 2000) must preserve a method of communication with the legacy 5.5 replication partners. The SRS enables this communication by appearing to the other Exchange 5.5 servers as simply another Exchange 5.5 server.

The need to rehome the existing Exchange 5.5 Directory Replication Connectors (DRCs) as bridgehead servers can be avoided by first upgrading the bridgehead servers between the Exchange 5.5 sites. When the bridgehead servers are upgraded from 5.5 to Exchange 2000, the CCAs that were configured in the 5.5 environment will automatically have their targets remapped to the newly upgraded SRS-enabled Exchange 2000 server.

Following the upgrade, the Site Consistency Checker (SCC) will perform a review of the entire replication topology between all the sites that it knows about. Using the information gathered in the review, the SCC will determine the best routes between the sites for the relay of information. Using this information, the SRS will disable DRC connections in favor of CCAs. This is because attribute-based replication is more efficient than object-based replication.

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