Active Directory Subnets, Sites

Active Directory Subnets

A single, physical network can be broken into smaller segments called subnets in a process called subnetting. Each subnet on a network is connected by routers. Every device in a network, whether it’s a domain controller (DC), a server, or a client, must belong to a particular subnet. By using subnets, an organization won’t need to acquire a new network number through its ISP.

When an organization deploys Active Directory (AD), it needs to create subnet objects for each subnet that exists in its overall network infrastructure. Each subnet object is then associated with a single site object within AD.

Active Directory Sites

A site object is made up of one subnet or a group of subnets connected by high-speed links. When promoting DCs, they are placed within a site (called Default-First-Site-Name) which gets created automatically. If additional sites are created, DCs can then be moved between sites.

An organization with offices in different geographical locations may find it beneficial to create sites for the following reasons:

1. Authenticating and authorizing users can be managed locally as much as possible.
2. Replication traffic can be streamlined and unnecessary network traffic can be avoided during business hours.

Client computers will always attempt to get their AD services from DCs that are within their same site before contacting DCs in other sites. This enables more efficient use of network bandwidth.

How to create a new site  

The following steps illustrate how to create an AD site:

• Go to Start → Administrative Tools → Active Directory Sites and Services. The Active Directory Sites and Services Window opens.
• In the left pane, right click Sites and click on New Site.
• Give the new site a suitable name. Select DEFAULTIPSITELINK, and click OK.

DC Locator

The process that a client computer/application uses to contact the closest available domain controller within an AD Domain is called the “DC Locator Process”. DC Locator is an algorithm that runs in the context of the Net Logon service on the client computer. It relies on DNS resolution and AD sites and subnets configuration for the identification.

DC locater is critical because:

• Sites are often linked by slow network connections which might cause slowness with cross-site communication with Active Directory.
• It minimizes the impacts when a Domain Controller is not available.
• It reduces unnecessary network traffic between sites by locating the closest Domain Controller.

Ref: https://servergurunow.wordpress.com/2017/10/14/dc-locator-process-2/#:~:text=The%20process%20that%20a%20client,service%20on%20the%20client%20computer.