Answer:
DNS-based Authentication of Named Entities .
Explanation:
While realizing how one of the DNS servers could have been affected. He thinks an intruder is targeting a stored DNS record for his domain.
So, the DNS-based Named Entities Authentication in Windows Server 2016 should be used on the user's DNS server to try to prevent a man-in-the-middle attempt from which an intruder changes his stored DNS record for the user's domain.