Q1 (70) Choose the DNS server setting that will prevent an existing host and its IP address...
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(70)**
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 a mechanism that replicates DNS zone data between authoritative DNS servers. Unrestricted zone transfers allow attackers to enumerate all hosts and their IP addresses in a domain (zone enumeration/DNS enumeration attack). By controlling the source of zone transfers—allowing them only from trusted secondary nameservers—you prevent unauthorized hosts from discovering the domain's infrastructure. Options A, C, and D address mail relay, CGI directory restrictions, and directory listing respectively, which are unrelated to DNS host/IP visibility.
Step-by-step Derivation:
The question asks what DNS setting prevents hosts and IPs from being discovered. Zone transfers (AXFR/IXFR queries) expose the complete DNS zone file to anyone who can query. Restricting zone transfers by source IP ensures only legitimate secondary nameservers can pull zone data, blocking reconnaissance attacks that enumerate all hostnames and addresses. This is a critical DNS security practice.