Exclude name suffixes from routing to a local forest

To exclude name suffixes from routing to a local forest

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.
On the Name Suffix Routing tab, under Name suffixes in the x.x forest, click the unique name suffix for which you want to exclude the routing status, and then click Edit.
In Name suffixes to exclude from routing to x.x, click Add, type a Domain Name System (DNS) name suffix that is subordinate to the unique name suffix, and then click OK.

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.
XOX
When you exclude a name suffix, all children of that DNS name will also be excluded.
To view a log of name suffixes, DNS names, NetBIOS names and the status associated with this trust, click Save As. This log can assist you in troubleshooting authentication problems.
For information about trusts, see Related Topics.