Starting 15 April 2019, AD Connector instances running on Windows Server 2003 and Windows Server 2008 (prior to SP2) will no longer be supported. On other Windows Server versions, you will need to ensure that TLS 1.2 has been enabled to securely run the AD Connector.
If you are running the AD Connector on Windows Server 2003 or Windows Server 2008 (prior to SP2), you will need to re-install the service on a more recent version of Windows Server and enable TLS 1.2.
Instructions to enable TLS 1.2 are provided below:
Windows Server 2008 SP2 : TLS 1.2 is not supported by default. If you have not already added support, follow instructions at https://support.microsoft.com/en-us/help/4019276/update-to-add-support-for-tls-1-1-and-tls-1-2-in-windows
Windows Server 2008 R2/Windows 7 and Windows Server 2012:
TLS 1.2 is supported but not enabled by default. If you have not already enabled this, follow instructions at https://support.microsoft.com/en-ph/help/3140245/update-to-enable-tls-1-1-and-tls-1-2-as-default-secure-protocols-in-wi
Windows Server 2012 R2, Windows Server 2016 and Windows Server 2019: TLS 1.2 is enabled by default.
Note: This pre-requisite applies only to the server running the AD Connector. If the AD Connector is not installed directly on the Domain Controller, there is no restriction on the domain functional level.