Q1 /20 Choose the DNS server setting that will prevent an existing host and its IP address...
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/20
Choose the DNS server setting that will prevent an existing host and its IP address from being known.
Show answer & explanation
Zone transfers are the mechanism by which DNS records (including host names and their IP addresses) are replicated between DNS servers. Controlling the access source of zone transfers restricts who can retrieve the complete DNS database, preventing unauthorized disclosure of host and IP mappings. Options A, C, and D relate to mail relay, CGI execution, and web directory listing respectively—none of which directly control DNS information exposure.
Step-by-step Derivation:
The question asks which DNS setting prevents hosts and IPs from being known. Let's analyze each option:
A) Third-party mail relay prohibition → Controls SMTP relay behavior, not DNS record disclosure.
B) Control zone transfer access → Zone transfers (AXFR/IXFR queries) allow complete DNS database replication. Restricting this prevents attackers from enumerating all DNS records including host-to-IP mappings. This directly answers the question.
C) CGI program directory restriction → Web server security, unrelated to DNS information disclosure.
D) Directory file name display prohibition → Web server directory listing control, not DNS security.
Conclusion: Option B is correct. Controlling zone transfer access sources is the DNS security control that prevents unauthorized access to host and IP address information.