COMException: The server is not operational

Recently there were a couple of network changes done at our client’s side which we weren’t aware of and ultimately it led to a downtime for CRM application. Users were not able to log-in to CRM and instead were getting an error which read as

CrmException: Failed to get priv user group information. k = 1b3b9610-36e3-e111-8aef-0050568b60d0 privUserGroupId: 47cbacdc-081f-4457-850f-bc66ef3a2137, localSystemAdGuid: 0005972b-bd43-4de4-8364-51f4b3ef27a8, Exception: System.Runtime.InteropServices.COMException: The server is not operational.

Upon researching a bit, it was clear that the issue was somehow related to Domain Controller which was not able to route any of the user requests thus none of users were able to get authenticated and get into the system. This is how we managed to fix it.
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