This section discusses the methods of replication between sites. It also tracks the changes to the object replication attributes. Every step discussed here can be tested in your own environment, and object replication states can be tracked using the Administrator program in raw mode.
In the following example, an object is created in the NAmerica-W site and replicated to the NAmerica-E bridgehead server. Eventually it will replicate to the downstream servers in the NAmerica-E site. This section will discuss the method used by replication in both instances and how that method is determined based on the naming context replication attributes.
A mailbox on server SanFrancisco01 is created with the directory name of Maria Black in site NAmerica-W. This new mailbox object has the following object replication attributes on server SanFrancisco01.
| Object replication attribute | Value |
| Obj-Dist-Name | /o=Ferguson&Bardell/ou=NAmerica-W/cn=Recipients/cn=Maria Black |
| DSA-Signature | D6149C3A935FD111AAEE00C04FB68E14 |
| USN-Changed | 1489 |
| USN-Created | 1489 |
| USN-Source | 1489 |
This object was created in the /o=Ferguson&Bardell/ou=NAmerica-W
naming context. The SanFrancisco01 server has only one replica link attribute
in its /o=Ferguson&Bardell/ou=NAmerica-W naming context. SanFrancisco01
has a Reps-To-Ext attribute with server Boston01 listed in the following
format: EX:/o=Ferguson&Bardell/ou=NAmerica-E/cn=Configuration/cn=Servers/cn=Boston01/cn=Microsoft DSA
This means that for this naming context, changes are sent to the Boston01 servers directory on request. Now, look at this naming context on the Boston01 server.
The Boston01 server has a value on the Reps-From field listing server SanFrancisco01. This value says changes are requested from the directory service on SanFrancisco01. It also provides other important information. For example, the Periodic Sync option is selected, which says changed information is requested based on the Period-Rep-Sync-Times attribute value. The Init Sync option is selected, which states that change requests are made on this naming context at directory startup. The Mail replica option is selected, which states that this naming context is replicated using a mail transport rather than RPC.
The USN value presented here is the last USN that was successfully replicated to this server for this naming context. What that means is that changes are requested from server SanFrancisco01 will have a higher USN number than 1485. The DSA-Signature is important uniquely identifies the replicating server in the organization.
Take a closer look at Period-Rep-Sync-Times before continuing with the replication process. The value of Period-Rep-Sync-Time is the same as the schedule specified for the Directory Replication object.
It is important to understand how the values that each Directory Replication Connector in the two sites place in this field affects replication. For example, the schedule for the Directory Replication Connector in site NAmerica-E is set to replicate every two hours. The Directory Replication Connector in site NAmerica-W is set to Always (every 15 minutes). Therefore, site NAmerica-E will only request changes from the NAmerica-W site at the scheduled times.
Note You should not set replication to Always in a production environment unless near real-time replication is required and there is sufficient bandwidth and CPU available to handle the overhead.
It is important to remember that the NAmerica-W naming context is read-only within the NAmerica-E site. That means if site NAmerica-E changes the replication schedule, that change needs to be replicated to site NAmerica-W and replicated back to site NAmerica-E for the change to take effect for the /o=Ferguson&Bardell/ou=NAmerica-W naming context. In other words, there can be some latency between the schedule being changed and the schedule taking effect.
Continuing with the replication of the Maria Black mailbox object, it has been created on server SanFrancisco01 in the /o=Ferguson&Bardell/ou=NAmerica-W naming context. There is an entry on the Reps-From attribute for this naming context on server Boston01. Therefore, are requested changes for this naming context, based on the Period-Rep-Sync-Times schedule from server SanFrancisco01 as follows:
At this point, the replicated Maria Black mailbox object on server Boston01 in site NAmerica-E has the following object replication attributes on server Boston01.
| Object replication attributes | Value |
| Obj-Dist-Name | /o=Ferguson&Bardell/ou=NAmerica-W/cn=Recipients/cn=Maria Black |
| DSA-Signature | D6149C3A935FD111AAEE00C04FB68E14 |
| USN-Changed | 2037 |
| USN-Created | 2037 |
| USN-Source | 1489 |
DSA-Signature is provided by server SanFrancisco01 because it was the last directory to modify the object. USN-Changed and USN-Created are 2037, new values unique to server Boston01. Finally, USN-Source is 1489, the USN-Changed value from server SanFrancisco01. Replication is complete between the two servers in different sites. Also of interest is the new USN value on the Reps-From attribute. Note that it has been updated to reflect that server Boston01 has received changes up to USN 1489.
Now that the object has been successfully replicated to the NAmerica-E site, it must be replicated to other servers within the site. A look at the naming context replication attributes of the /o=Ferguson&Bardell/ou=NAmerica-W shows that server Boston01 is responsible for replicating the content of this naming context to server NewYork01.
Based on the fact that server NewYork01 is listed in the Reps-To field, we know that we will replicate this object using intrasite replication methods.
At this point, the mailbox object Maria Black now exists on the NewYork01 server with the following replication attributes.
| Object replication attributes | Value |
| Obj-Dist-Name | /o=Ferguson&Bardell/ou=NAmerica-W/cn=Recipients/cn=Maria Black |
| DSA-Signature | D6149C3A935FD111AAEE00C04FB68E14 |
| USN-Changed | 1360 |
| USN-Created | 1360 |
| USN-Source | 2037 |
Note that the DSA-Signature is that of server SanFrancisco01. This is because that was the last directory to modify the object. Also note that the USN-Source is the USN-Changed number from Boston01. That is because server Boston01 was the last remote directory to replicate the change to us. It does not matter that it was not the directory that made the change, only that it was the last directory to replicate the object to us.
Replication of the object throughout the organization is complete.