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Zorluk: OrtaTroubleshooting DNS and Name Resolution Services

A systems engineer executes the following command to diagnose a connection failure to an internal application server:

text
$ dig @10.0.4.15 app.internal.net A

;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 48219
;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 1

;; QUESTION SECTION:
;app.internal.net. IN A

;; AUTHORITY SECTION:
internal.net. 3600 IN SOA ns1.internal.net. admin.internal.net. ( 2026072601 7200 3600 1209600 3600 )

Based on the output snippet, which of the following best explains why no IP address was returned for the query?

  1. The DNS server is reachable and authoritative for the domain, but no resource record matching the requested host name and type exists.Cevap
  2. B
    The query failed because the client requested an IPv4 A record when the server only supports IPv6 AAAA record resolution.
  3. C
    The command line output indicates that the local client resolver cache has overwritten the authoritative DNS server response.
  4. D
    The DNS query timed out because UDP port 53 traffic was blocked by an intermediate network firewall.

Cevap

The DNS server is reachable and authoritative for the domain, but no resource record matching the requested host name and type exists.
The correct response identifies that the server successfully answered the query with status NOERROR and zero answer records, supplying the zone SOA record in the authority section. This specific combination signifies a NODATA response, proving the server is authoritative for internal.net but no A record exists for app.internal.net.

Adım Adım Çözüm

1
Examine the dig response header status and section counts
The header shows status: NOERROR, QUERY: 1, ANSWER: 0, AUTHORITY: 1.
Understanding the header flag summary reveals whether the query succeeded at the protocol layer and if any answer records were returned.
2
Analyze the AUTHORITY section contents
The AUTHORITY section contains the Start of Authority (SOA) record for internal.net.
When a DNS server returns NOERROR with 0 answer records alongside an SOA record, it indicates a NODATA condition (the domain exists on the authoritative server, but the requested host 'app' does not have an A record).
3
Differentiate NODATA from network transport failures or local resolver issues
Network communication succeeded on port 53 and direct query was made to 10.0.4.15.
Eliminates firewall blocking (which causes timeouts) and local cache interference (since dig directly queries the specified IP).

Anahtar Kavram

Interpreting dig output sections and DNS NODATA / SOA responses during resolution troubleshooting.
Tahmini Süre:1m 15s
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Troubleshooting DNS and Name Resolution Services

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