(Optional) Review the various trust types and understand forest trust concepts.

Trust types; Forest trusts; When to create a forest trust; Accessing resources across forests; Routing name suffixes across forests

Ensure that Domain Name System (DNS) is properly set up.

If there is a root DNS server that can be made the root DNS server for both of the forest DNS namespaces, make it the root server by ensuring that the root zone contains delegations for each of the DNS namespaces. Also, update the root hints of all DNS servers with the new root DNS server.

If there is no shared root DNS server and the root DNS servers for each forest DNS namespace are running a member of the Windows Server 2003 family, configure DNS conditional forwarders in each DNS namespace to route queries for names in the other namespace.

If there is no shared root DNS server, and the root DNS servers for each forest DNS namespace are not running a member of the Windows Server 2003 family, configure DNS secondary zones in each DNS namespace to route queries for names in the other namespace.

Verify a zone delegation using the nslookup command; Update root hints on the DNS server; Configure a DNS server to use forwarders; Add a secondary server for an existing zone; Namespace planning for DNS

Set the forest functional level in both forests to Windows Server 2003.

Raise the forest functional level

Create a forest trust.

Create a forest trust