Active Directory Site design, 3 things to consider…

Mar 17th, 2009

Some newbie to Active Directory structure and design submitted a question on one of the forums to know how sites works in relation to his entire infrastructure, because his company has acquired another firm in a remote location. I thought I should post my response in my blog, just in case same question might came up again.

Active Directory Replication:Each Windows Server Domain controller holds a copy of the Active Directory database and each domain controller must be updated when a change occurs. This process of sending updates between domain controllers is called replication. Replication ensures that Active directory is always up to date and current across the entire network Active Directory environment.

Active Directory Replication Methods:Within a windows Active Directory environment, there are two methods of replication occurrence, namely intrasite and intersite replications. Intrasite replication is replication within an active directory site and replication is automatically created by default and connection objects are automatically setup among domain controllers within the site to facilitate frequent replication. Intersite replication involves replication across sites, sometimes across WAN links. This before starting to design and configure an intersite replication, it is worthwhile to take into consideration three most important criterion. Site Cost, AD Servers, and AD replications. Also, sometimes, Administrators are caught in the middle between data accuracy and time when deciding how to reduce latency (the time required to replicate data from domain controller to domain controller and site to site).

*Cost: Active Directory uses site costs to determine which site link have priority over the other link. Site links with lower costs have priority or precedence over that with higher costs.

*Schedule: Intersite replication normally require a schedule to determine replication occurrence. The main purpose for a schedule is to avoid replication from using too much bandwidth especially at peak production hours.

*AD Servers: It is always advisable to have at least one Global Catalog and a DNS server on each site to ensure good replication performance. Although having a GC on a site may increase replication traffic, it will eventually decreases users traffic over the Wide Area Network links, those leaving room for replication. Placing a DNS server on the site and forcing users to use it for DNS service, will also reduce WAN traffic.

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