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Difficulty: MediumUtilizing Command-Line Network Troubleshooting Utilities

A network administrator is troubleshooting an issue where workstation users are directed to an old server IP address for an internal web application hosted at `app.corp.internal`. The administrator suspects the local DNS server (`192.168.1.1`) is returning a cached, non-authoritative record. Which command should the administrator run to query the authoritative DNS server at `10.100.1.10` directly for the IPv4 address record?

  1. nslookup app.corp.internal 10.100.1.10Answer
  2. B
    dig -t AAAA app.corp.internal @10.100.1.10
  3. C
    nslookup -port=80 app.corp.internal 10.100.1.10
  4. D
    dig app.corp.internal -server 10.100.1.10

Answer

The command `nslookup app.corp.internal 10.100.1.10` directly queries the authoritative DNS server for the standard IPv4 address (A record) of the specified host.
The command `nslookup app.corp.internal 10.100.1.10` instructs `nslookup` to send a default IPv4 (A record) lookup query for `app.corp.internal` directly to the specified server address `10.100.1.10`, bypassing the host's default configured DNS server.

Step-by-Step Solution

1
Identify the required utility and target host name.
The target domain to resolve is `app.corp.internal` for standard IPv4 resolution (A record).
The administrator needs to verify the IPv4 mapping returned directly by the authoritative server.
2
Determine the proper syntax to bypass the default local resolver.
Appending `10.100.1.10` after the hostname in `nslookup` sends the query directly to `10.100.1.10`.
This bypasses cached or non-authoritative entries stored on the local DNS server (`192.168.1.1`).
3
Verify command flags and protocol ports.
`nslookup app.corp.internal 10.100.1.10` uses standard DNS port 53 and queries for an A record by default.
No additional flags altering port numbers or record types to IPv6 are needed.

Key Concept

Direct DNS Querying via Command-Line Utilities
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Topics

Utilizing Command-Line Network Troubleshooting Utilities

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