Exchange Active Directory Provider found no global catalog servers in the local site or external sites. The sites are specified in the associated events. This can cause services startup failure or halting of mail flow. Therefore, it should be investigated immediately.

This may be caused by the following conditions:

• All domain controllers are down or are not suitable
  
  
• Network problems prevent the Exchange computer from contacting the domain controllers
  
  
• Permission problems
  
  
• Configuration errors
  
  

To resolve this event, do one or more of the following:

• Verify that at least one global catalog exists in the forest and that it is reachable from the Exchange server on port 3268. If there are no global catalogs in the forest, use the Sites and Services MMC snap-in to promote a domain controller to a global catalog server.
  
  
• Verify that DNS is configured correctly on the Exchange server and that the configured DNS servers are functional and reachable.
  
  
• Use the nltest /dsgetdc: <domain> /site:<site name> command to verify that a global catalog server can be located in the specified sites. Look for the global catalog server flag in the nltest output. The NLTest tool is installed with the Windows support tools.
  
  
• Check the Application log for related events. The detail in other MSExchange ADAccess events and other events may help determine the root cause of this warning. Increase diagnostic logging for the MSExchange ADAccess\Topology category to Lowest or higher. For detailed information about how to increase logging, see Manage Diagnostic Logging Levels.
  
  
• If MSExchangeADAccess Event ID 2080 is logged, no suitable global catalogs may have been found when initial topology discovery was completed. Review that event to determine which domain controllers have been contacted and if they are unsuitable for any reasons. Correct any problems as indicated by the event description. For more information, see Microsoft Knowledge Base article 316300, Event ID 2080 from MSExchangeDSAccess.
  
  
• If MSExchangeADAccess Event ID 2070 is logged, a global catalog may be down or is unreachable. Review the event for more information about why each domain controller is not suited. DSAccess found no suitable global catalogs when initial topology discovery was completed.
  
  
• Use the Ping or PathPing command-line tools to test basic connectivity. Use Ping to isolate network hardware problems and incompatible configurations. Use PathPing to detect packet loss over multiple-hop trips. For more information, see Microsoft Knowledge Base article 325487, How to troubleshoot network connectivity problems.
  
  

If you are not already doing so, consider running the Exchange tools created to help you analyze and troubleshoot your Exchange environment. These tools can help make sure that your configuration aligns with Microsoft best practices. They can also help you identify and resolve performance issues, improve mail flow, and better manage disaster recovery scenarios. To run these tools, go to the Toolbox node of the Exchange Management Console. To learn more about these tools, see Managing Tools in the Toolbox.