Q1 /20 Choose the DNS server setting that will prevent an existing host and its IP address...
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Choose the DNS server setting that will prevent an existing host and its IP address from being known.
Show answer & explanation
A zone transfer is the mechanism by which DNS information (including all host records and their IP addresses) is replicated from a primary DNS server to secondary servers. By controlling who can access zone transfers (restricting them to authorized secondary DNS servers only), you prevent unauthorized parties from obtaining a complete inventory of all hosts and their IP addresses. Options A, C, and D relate to mail server security, web server security, and web directory listing respectively—none address DNS host enumeration.
Step-by-step Derivation:
In DNS security, a zone transfer (AXFR query) dumps the entire zone database containing all DNS records. An unrestricted zone transfer allows attackers to discover all hosts, subdomains, and their associated IP addresses. Controlling the accessing source of zone transfers (typically via ACLs limiting transfers to authorized secondary DNS servers) is the standard mitigation. Option A (third-party mail relay) prevents spam/email abuse. Option C (CGI restrictions) prevents arbitrary code execution on web servers. Option D (file listing) prevents directory traversal on web servers. Only option B directly prevents host and IP disclosure at the DNS level.