Install and configure Azure AD Connect

 In this blog, I will discuss a common scenario where Exchange servers are running an outdated Cumulative Update (CU) version and need to be upgraded. Generally, this process is straightforward unless there are .NET compatibility issues that could impact the entire upgrade.

Exchange's Cumulative Update (CU) support policy

According to the Exchange servers model since Exchange 2013 and for all future on-premises versions, only the latest two CU versions are supported:

A CU will be supported for a period of three 3 months after the release date of the next CU. For example, if CU1 is released on March 1 and CU2 is released on June 1, CU1 support will end on September 1.

As you probably know, Exchange requires the .NET Framework, which must be supported by the Cumulative Update (CU) version you are running. For the further information, please visit the Exchange supportability matrix.

https://docs.microsoft.com/en-us/Exchange/plan-and-deploy/supportability-matrix?view=exchserver-2019#microsoft-net-framework

When do I encounter an issue?

Just think about that our customer is running Exchange 2016 CU12 with .NET 4.7.2 installed on their servers. This customer wants to upgrade their servers to Exchange 2016 CU23(currently the latest version). According to the Exchange supportability matrix, the only .NET Framework version supported by Exchange 2016 CU23 is .NET Framework 4.8.

Now this customer has two options:

• To be on the safe side, they should install Exchange 2016 CU13 or CU14, which support .NET 4.7.2. Then, install .NET 4.8 (which supports Exchange 2016 CU13-CU23) and upgrade to Exchange 2016 CU23. The advantage of this approach is that the environment remains in a supported state throughout the process. However, the disadvantages are that you might not have access to the previous CU (such as CU14 in this example) since only the latest CUs are publicly available, and the installation process can be lengthy, especially in a large Exchange environment with many servers.
• The other option is to install .NET 4.8, putting the environment in an unsupported state according to the Exchange supportability matrix, and then upgrade to Exchange 2016 CU23.

How can the upgrade be done in the safest way?

Consider the following important statement from the Exchange supportability matrix article:

“When upgrading Exchange from an unsupported CU to the current CU, and if no intermediate CUs are available, you should first upgrade to the latest version of .NET supported by Exchange and then immediately upgrade to the current CU. This approach does not eliminate the necessity of keeping your Exchange servers up-to-date with the latest supported CU. Microsoft does not guarantee that this method will prevent upgrade failures, which might necessitate contacting Microsoft Support Services.” 

To upgrade Exchange to the latest CU, follow these steps:

1: Place the Exchange server into Maintenance Mode.

Click here> How to Place the Exchange Server into Maintenance Mode

2: Prepare for Cumulative Update

Generally, you need to install the following:

• NET framework 4.8+
• Visual C++ Redistributable for Visual Studio 2012

3: Install RSAT-ADDs Feature

Open Powershell (Run as Administrator) and install this feature.

Install-windows feature RSAT-ADDS

Restart the server after installation

4: Prepare Active Directory Schema

Before you can extend the schema, your account needs to be a member of the Schema Admins and Enterprise Admins security groups.

Run Command Prompt as administrator and put the following command

I:\Setup.exe /IAcceptExchangeServerLicenseTerms_DiagnosticDataOFF /PrepareSchema

5: Prepare Active Directory

Run Command Prompt as administrator and put the following command

I:\Setup.exe /IAcceptExchangeServerLicenseTerms_DiagnosticDataOFF /PrepareAD

6: Prepare Active Directory domains

Run Command Prompt as administrator and put the following command

I:\Setup.exe /IAcceptExchangeServerLicenseTerms_DiagnosticDataOFF /PrepareAllDomains

7: Install Cumulative Updates 

After the pre-requisites on your server, mount the downloaded Cumulative Update ISO image.

Restart Server after the installation.

8: Testing

Check the event logs by filtering for errors and warnings. If there are errors, make sure to troubleshoot and fix them.

9: Remove Server from Maintenance Mode

Click here> How to Remove Server from Maintenance Mode

10: Install Pending Security Updates 

Check and install if you see any pending security updates

Install Cumulative Update on all Exchange Servers

If you have more than one Exchange Server running in the organization then do the same steps on all the Exchange Servers.

Conclusion:

In this blog, you have explored the process of upgrading the Cumulative Update (CU) on an Exchange Server. We walked through the key steps required to ensure a smooth and successful upgrade, including the preparation of your environment and the careful execution of upgrade commands. Understanding these steps is crucial for maintaining the stability and performance of your Exchange Server. Remember to always back up your data before proceeding with any updates and to review the release notes for any specific instructions or changes. By following these guidelines, you can confidently keep your Exchange Server up-to-date and running efficiently.

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