2.2.1 Implement only one primary function per server to prevent functions that require different security levels from co-existing on the same server. (For example, web servers, database servers, and DNS should be implemented on separate servers.)

Note: Where virtualization technologies are in use, implement only one primary function per virtual system component.

2.2.1.a Select a sample of system components and inspect the system configurations to verify that only one primary function is implemented per server.
2.2.1.b If virtualization technologies are used, inspect the system configurations to verify that only one primary function is implemented per virtual system component or device.

If server functions that need different security levels are located on the same server, the security level of the functions with higher security needs would be reduced due to the presence of the lower-security functions.

Additionally, the server functions with a lower security level may introduce security weaknesses to other functions on the same server. By considering the security needs of different server functions as part of the system configuration standards and related processes, organizations can ensure that functions requiring different security levels don’t co-exist on the same server.