Enable or disable an existing name suffix from routing

To enable or disable an existing name suffix from routing

Open Active Directory Domains and Trusts.
In the console tree, right-click the domain node for the domain you want to administer, and then click Properties.
On the Trusts tab, under either Domains trusted by this domain (outgoing trusts) or Domains that trust this domain (incoming trusts), click the forest trust that you want to administer, and then click Properties.
Click the Name Suffix Routing tab, under Name suffixes in the x.x forest, do one of the following:

To enable a name suffix, click the suffix that you want to enable, and then click Enable. If the Enable button appears dimmed, then the name suffix is already enabled.
To disable a name suffix, click the suffix that you want to disable, and then click Disable. If the Disable button appears dimmed, then the name suffix is already disabled.

Notes

To perform this procedure, you must be a member of the Domain Admins group (in the forest root domain) or the Enterprise Admins group in Active Directory, or you must have been delegated the appropriate authority. As a security best practice, consider using Run as to perform this procedure.
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When you disable a name suffix, all children of that DNS name will also be disabled.
You cannot enable a name suffix that is in conflict. If the conflict is with a local UPN name suffix, then you need to remove the local UPN name suffix before you can enable the routing name. If the conflict is with a name claimed by another trust partner, then you will need to disable the name in the other trust before it can be enabled for this trust.
For information about trusts, see Related Topics.