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Difficulty: MediumDNS Infrastructure and Record Types

A network administrator is troubleshooting a reverse DNS resolution failure for an internal database server with IP address 192.168.10.45192.168.10.45. The administrator executes a diagnostic command on a client workstation and receives the following output:

text
$ dig -x 192.168.10.45

;; QUESTION SECTION:
;45.10.168.192.in-addr.arpa. IN PTR

;; ANSWER SECTION:

;; AUTHORITY SECTION:
10.168.192.in-addr.arpa. 3600 IN SOA ns1.corp.internal. admin.corp.internal. 2026072701 7200 3600 1209600 3600

;; SERVER: 192.168.10.2#53(192.168.10.2)

Based on the diagnostic output, which of the following DNS configuration changes is required on the authoritative server to resolve the query successfully?

  1. Add a PTR record mapping 45.10.168.192.in−addr.arpa.45.10.168.192.in-addr.arpa. to the database server's fully qualified domain name (FQDN).Answer
  2. B
    Add an A record mapping the database server's hostname directly to the IP address 192.168.10.45192.168.10.45 in the forward lookup zone.
  3. C
    Configure a dynamic CNAME record to map port 53 DNS query requests directly to port 80 HTTP services.
  4. D
    Reconfigure the client resolver to force TCP transport instead of UDP for standard reverse query lookups on port 53.

Answer

Add a PTR record mapping 45.10.168.192.in−addr.arpa.45.10.168.192.in-addr.arpa. to the database server's fully qualified domain name (FQDN).
The `dig -x` diagnostic tool requests a reverse DNS lookup for an IP address. The command output shows a query for `45.10.168.192.in−addr.arpa.45.10.168.192.in-addr.arpa.`. Because the server returns an AUTHORITY section with an SOA record but no ANSWER section, the reverse lookup zone is present on the server, but the specific PTR record for host address 192.168.10.45192.168.10.45 has not been configured.

Step-by-Step Solution

1
Analyze the command and query type
The `dig -x 192.168.10.45` command initiates a reverse DNS lookup, requesting a Pointer (PTR) record for the domain `45.10.168.192.in−addr.arpa.45.10.168.192.in-addr.arpa.`.
Reverse DNS resolution queries the `.in-addr.arpa` domain hierarchy using octets reversed.
2
Inspect the query output sections
The ANSWER section is empty, while the AUTHORITY section provides the SOA record for the zone `10.168.192.in-addr.arpa.`.
An empty ANSWER section with an authoritative SOA response indicates the server is authoritative for the zone, but no resource record matching `45.10.168.192.in−addr.arpa.45.10.168.192.in-addr.arpa.` exists.
3
Identify the required record creation
Create a PTR record for host 4545 within the 10.168.192.in−addr.arpa.10.168.192.in-addr.arpa. reverse zone pointing to the canonical FQDN.
PTR records perform IP address-to-hostname resolution.

Key Concept

Reverse DNS Resolution and PTR Records
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Topics

DNS Infrastructure and Record Types

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