You can design an external namespace that is visible to Internet users and computers. You can also design an internal namespace that is visible only to users and computers that are in your internal network.
Organizations that require an Internet presence and an internal namespace must deploy both an internal and an external DNS namespace and manage each namespace separately. In this case, we recommend that you make your internal domain a subdomain of your external domain. For example, an organization that has an external domain name of contoso.com might use the internal domain name corp.contoso.com. Using an internal domain that is a subdomain of an external domain has the following advantages:
Requires you to register only one name with an Internet name authority even if you later decide to make part of your internal namespace publicly accessible.
Ensures that all of your internal domain names are globally unique.
Simplifies administration by enabling you to administer internal and external domains separately.
Allows you to use a firewall between the internal and external domains to secure your DNS deployment.
If you want to deploy an AD DS domain for each division in your organization, you can use your internal domain as a parent for additional child domains that you create to manage those divisions. Child domain names are immediately subordinate to the domain name of the parent. For example, a child domain for a manufacturing division that you add to the us.corp.contoso.com namespace might have the domain name manu.us.corp.contoso.com.
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