You can use Active Directory Domains and Trusts to administer forest trusts.

• Understanding When to Create a Forest Trust
  
  
• Checklist: Create a Forest Trust
  
  
• Create a Forest Trust
  
  
• Change the Routing Status of a Name Suffix
  
  
• Enable or Disable an Existing Name Suffix from Routing
  
  
• Exclude Name Suffixes from Routing to a Local Forest