How to Change the Percentage of Domain Controllers Req'd for Exchange Functions

Email is the lifeblood of any business and is a major way of communicating for individuals. Every online order, bank deposit using an app, and important communication often involves email. With reliable email systems, we never consider what we would do without it. Unfortunately, there are times when things happen and servers fail to respond or operate as expected. 

An Exchange 2013 or later server may stop passing email even if there is nothing wrong with it directly. This can happen when a number of available domain controllers cannot be contacted. If there are network or communication errors happening, changing the percentage of domain controllers required for normal Exchange functions will allow email to begin working again. NOTE: The default percentage of domain controllers required to be accessible for Exchange 2013 or later to function properly is 50%.

How to Change the Percentage of Domain Controllers Required for Exchange to Function Normally

Changing the percentage of domain controllers required by Exchange is a potential troubleshooting step along with other areas that should also be explored including:

• Verifying Exchange can be accessed both locally and from outside the firewall
• Checking the error logs in event viewer and fixing any applicable errors
• Event ID's #2069, #2060, #2070, and #2077 all refer to issues connecting to available domain controllers and likely mean changing the default percentage of required domain controllers will fix the issue. (Look for a reference to: Microsoft.Exchange.Directory.TopologyService in the error message).
• Checking to make sure there is enough disk space available for Exchange services and operation to run properly.
• Verifying all databases are currently mounted.
• Checking the health status of Active Directory to be sure it is in a healthy state.

To change the percentage of domain controllers required for Exchange to function properly: 

• Navigate to the Bin folder under Program Files, Microsoft, Exchange Server, Version number.
• Locate the "Microsoft.Exchange.Directory.TopologyService.exe.config" file.
  
  
  


• Right-click on the file and select "Edit", select "Notepad" if prompted for which program to use to open the file.
• In Notepad, look for the following entry: 
• 'MinPercentageOfHealthyDC = "50"'
• Change the number in quotes from 50 to whatever percentage desired but no lower than 10.
• To reduce the amount to 10%, the entry would look like: 'MinPercentageOfHealthyDC = "10"'
• Add this line below the aforementioned line: 'MinSuitableServer = "X"', where X is a number equal to or greater than 1. This entry sets the minimum amount of suitable servers to the number entered.
  
  
  


• Once all changes have been made, save the file.
• Restart the Microsoft Exchange Active Directory Topology service.

Changing the percentage of available domain controllers required for Exchange to function normally may bring email back online when other troubleshooting efforts have failed. This fix is best applied when legacy domain controllers are no longer operating properly, are not syncing with Active Directory correctly, or when network interruptions have recently or are currently occurring. Updating the required domain controllers allows Exchange operations to return to a stable and functioning state so email can operate even if other network issues exist. Once additional domain controllers are again available, Exchange will utilize them as if nothing changed and operations will continue normally.

As always, knowing more than one way to accomplish the same thing is imperative when it comes to technology!

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