Understanding Sites and Replication
Sites
A site is a combination of one or more IP subnets connected by a highly reliable and fast link to localize as much network as possible.
With Active Directory, sites are not part of the namespace. When we browse the logical namespace, we see computers and users grouped into domains and OUs, not sites.
Site and Domain relationship
Domain Controllers
A domain controller is a server that contains a writable copy of all Active Directory database, participates in Active Directory replication for that domain, and controls access to network resources.
We can manage user accounts, network access, shared resources, site topology and other directory objects from any domain controller in the forest.
Concept of Replication
Replication is the process of updating the changes made to a domain controller among all domain controllers within the domain.
The information stored in the directory (in the Ntds.dit file) is logically partitioned into four categories. Each of these information categories is referred to as a directory partition.
The directory contains the following partitions:
(i) Schema
(ii) Configuration
(iii) Domain
(iv) Application Directory
(i) Schema data: This partition defines the objects that can be created in the directory and the attributes those objects can have. This data is common to all domains in a forest and is replicated to all domain controllers in a forest.
(ii) Configuration data: This partition describes the logical structure of the deployment, including data such as domain structure or replication topology. This data is common to all domains in a forest and is replicated to all domain controllers in a forest.
(iii) Domain data: This complete, detailed information about every object in the domain is replicated only to all domain controllers within this domain.
(iv) Application Directory data: This partition stores dynamic application-specific data in Active Directory without significantly affecting network performance by enabling you to control the scope of replication and the placement of replicas.
| Parameters | Intrasite Replication | Intersite Replication |
| Compression | To save CPU time, replication data is not compressed. | To save WAN bandwidth, replication data greater than 50(KB) is compressed. |
| Replication model | To reduce replication latency, replication partners notify each other when changes need to be replicated and then pull the information for processing. | To save WAN bandwidth, replication partners do not notify each other when changes need to be replicated. |
| Replication frequency | Replication partners poll each other periodically. | Replication partners poll each other at specified intervals, only during scheduled periods. If updates are necessary, operations are scheduled to pull the information for processing. |
| Transport protocols | Remote procedure call (RPC). | IP or Simple Mail Transport Protocol (SMTP). |
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