Q

What should I know about subnets when removing sites from an AD environment?

Active Directory expert Laura E. Hunter tells a reader what to keep in mind when deleting subnets associated with sites being removed in an environment.

I am in the process of removing sites that exist in our environment. If I delete the subnets associated with these sites, do the workstation subnets automatically become part of the Default-First-Site again?
If you delete the subnets associated with a particular site, any clients associated with those subnets will no longer have a site membership, and will authenticate against any available domain controller. The exception to this is if you use "super-netting" to define your AD sites.

Let's say that you have SiteA, SiteB, and SiteC that correspond to the 10.10.1.0/24, 10.10.2.0/24, and 10.10.3.0/24 subnets, respectively. If you delete the 10.10.3.0/24 subnet, any clients using that IP range will randomly select a DC from one of the other two sites by default. Now let's say that you configure SiteA to contain two subnets: 10.10.0.0/16, and 10.10.1.0/24. As long as SiteC is associated with the 10.10.3.0/24 subnet,...

any clients in the .3 subnet will authenticate against SiteC. But if you delete the .3 subnet, those clients will now use the DCs in SiteA, since they fall under the "umbrella" of the 10.10.0.0/16 supernet.

This was first published in October 2007

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