Crucial Exams

CompTIA Linux+ XK0-006 (V8) Practice Question

A help-desk ticket says that some DNS queries are timing out after a recent rollout of DNSSEC validation on the company's caching resolver. A packet capture from a Linux workstation behind the corporate firewall shows this sequence:

  • The client sends a UDP query; the resolver replies with the TC flag set (response truncated).
  • The client immediately retries the same query over TCP port 53 but never receives a SYN-ACK.
  • When the user connects through a VPN that bypasses the firewall, the identical query succeeds.
  • Simple A-record lookups that fit in a single UDP packet continue to work normally.

Based on these observations, which configuration issue is most likely causing the failures?

  • The DHCP server handed out an incorrect default gateway, forcing the client to send DNS traffic to an unreachable network.

  • EDNS0 support has been disabled on the recursive resolver, preventing it from sending OPT records in queries.

  • The workstation's search domain list contains more than six entries, causing the resolver to discard DNSSEC responses.

  • The corporate firewall is filtering DNS traffic on TCP port 53, so truncated queries cannot be retried over TCP.

CompTIA Linux+ XK0-006 (V8)
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