XK0-005 practice question 10 of 10

An administrator is investigating why a Linux workstation is not resolving a website. The output of dig and nslookup shows that IPv4 resolution is…

An administrator is investigating why a Linux workstation is not resolving a website. The output of dig and nslookup shows that IPv4 resolution is working, but IPv6 resolution fails.

The administrator executes: nslookup -querytype=AAAA www.comptia.org Can't find www.comptia.org: No answer The workstation has a static entry in /etc/hosts: 104.18.99.101 www.comptia.org

Which of the following is the most likely cause?

Answer options

A: The static entry needs to be removed from /etc/hosts.

B: The remote website does not support IPv6, and the workstation requires it. Correct answer

C: The firewall needs to be modified to allow outbound HTTP and HTTPS.

D: The nameserver in /etc/resolv.conf needs to be updated to 8.8.8.8.

Correct Answer:

B. The remote website does not support IPv6, and the workstation requires it.

Explanation

The nslookup utility queries DNS servers directly via port 53 and bypasses local hostname resolution files such as /etc/hosts. The response "Can't find www.comptia.org: No answer" indicates that the DNS server responded successfully without an error code (NOERROR), but contained zero answer records for the requested AAAA (IPv6 address) query type. This result confirms that the DNS resolution pipeline is functioning properly, but the target domain name does not have configured IPv6 AAAA resource records. Consequently, the workstation cannot resolve an IPv6 address for the website because the remote web domain does not support IPv6 resolution.

Why Incorrect

A. nslookup queries configured DNS servers directly and ignores local entries in /etc/hosts, making the local static mapping irrelevant to DNS query results.
C. A firewall blocking HTTP/HTTPS traffic affects TCP network transport on ports 80/443, not DNS queries which returned a valid response from the DNS server.
D. The nameserver successfully responded with a valid "No answer" DNS reply, confirming the current server is reachable and functioning correctly without requiring server changes.

References

IETF RFC 3596: "DNS Extensions to Support IP Version 6" (https://doi.org/10.17487/RFC3596).

Red Hat Enterprise Linux 9 Networking Guide, Chapter 3: "DNS and Name Resolution Utilities".

BIND 9 Administrator Reference Manual, Section 6.2: "DNS Query Types and Resource Records".

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