A network technician receives reports that internal workstations are intermittently directed to an external IP address when resolving the internal hostname `app.corp.local`. To investigate, the technician executes `nslookup app.corp.local 10.0.4.10` from a CLI interface and receives the following output:
Server: internal-dns.corp.local
Address: 10.0.4.10
Non-authoritative answer:
Name: app.corp.local
Address: 203.0.113.88
Based on this output, which of the following is the most accurate analysis of the issue?
- The local DNS server returned a cached response from an external recursive lookup rather than answering authoritatively from its local primary zone file.Answer
- BThe DNS server at 10.0.4.10 is confirmed as the authoritative master for `corp.local` because its hostname is explicitly displayed under the initial Server header.
- CThe query failed to return internal records because `nslookup` defaults to requesting IPv6 AAAA records unless overridden with an explicit record type switch.
- DThe DNS lookup timed out and returned stale data because standard interactive DNS queries require TCP port 80 instead of UDP port 53.
Answer
The local DNS server returned a cached response from an external recursive lookup rather than answering authoritatively from its local primary zone file.
In DNS troubleshooting, a 'Non-authoritative answer' output from `nslookup` or `dig` signifies that the DNS server responding to the query does not maintain the authoritative zone file for the domain queried. Instead, the server obtained the record by querying external upstream servers recursively and cached the result. Returning an external IP address (`203.0.113.88`) for an internal domain under a non-authoritative banner indicates the server is resolving the domain via forwarders or cache rather than using a local primary domain zone.
Step-by-Step Solution
Key Concept
Interpreting nslookup output headers and distinguishing authoritative zone responses from cached recursive lookup results.