Exam 212-82 topic 1 question 26 discussion

Hayes, a security professional, was tasked with the implementation of security controls for an industrial network at the Purdue level 3.5 (IDMZ). Hayes verified all the possible attack vectors on the IDMZ level and deployed a security control that fortifies the IDMZ against cyber-attacks.
Identify the security control implemented by Hayes in the above scenario.