How are servers able to conduct a simple authentication check using DNS?

A.
Forward DNS lookup

B.
Reverse DNS lookup

C.
RARP

D.
Nslookup

Explanation:
A simple authentication check can be performed by checking what name corresponds to the IP address of the computer. This is done a reverse DNS-lookup, a name to IP lookup. If there is a corresponding RR record with appropriate name the simple authentication succeeds.
Incorrect Answers:
A: For a simple authentication check we should use a name to IP lookup, a reverse DNS lookup, not a Forward DNS lookup.
C: RARP (Reverse Address Resolution Protocol) does not use DNS.
D: NSLOOKUP is a user command for a user to check DNS server functionality. The command is not directly used by the operating system of the server, although the procedure being executed will be similar.