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 allow DNS replication between servers. Restricting zone transfer access prevents unauthorized parties (including attackers) from querying a DNS server for its full DNS records, which would reveal all hosts and their IP addresses within a zone. Options A, C, and D relate to mail relay, CGI execution, and web server directory listing respectively—none directly prevent DNS host/IP enumeration.
Step-by-step Derivation:
DNS zone transfer (AXFR queries) is a mechanism that replicates the entire DNS database from a primary to secondary DNS servers. If unrestricted, an attacker can perform a zone transfer to dump all DNS records (A records, MX records, etc.), revealing all hosts and their associated IP addresses. By controlling the accessing source of zone transfers (allowing only authorized secondary DNS servers), you prevent this information disclosure. The other options address different security concerns: A) mail relay (SMTP), C) CGI execution (web server), D) directory listing (web server)—none prevent DNS enumeration.