Great post from Alex Johnson on the difference between the discussion and requirements of CMMC practices.
“I want to offer some information to those who may be struggling with understanding what options are available to you regarding the implementation of NIST SP 800-171 and CMMC requirements or practices.
NIST SP 800-171 Section 2.2 contains the following:
“A discussion section follows each CUI security requirement providing additional information to facilitate the implementation and assessment of the requirements. This information is derived primarily from the security controls discussion sections in [SP 800-53] and is provided to give organizations a better understanding of the mechanisms and procedures used to implement the controls used to protect CUI. The discussion section is informative, not normative. It is not intended to extend the scope of a requirement or to influence the solutions organizations may use to satisfy a requirement. The use of examples is notional, not exhaustive, and not reflective of potential options available to organizations. “
The bottom line is that you have options. The discussions are not telling you exactly what you have to do. Rather, they are helping you to understand the essence of what the requirement is. There are a few discussions that are normative, but only a few.
A great example of this can be found in MP.2.119 (3.8.1). These assessment objectives require you to physically control and securely store media containing CUI. The discussion indicates that “physically controlling system media includes conducting inventories.” However, that is not a requirement based on NIST SP 800-171 Section 2.2.
I hope this helps some who may “extend the scope of a requirement” based on the discussion section.”