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Difficulty: MediumTroubleshooting DNS and Name Resolution Services

A systems engineer is troubleshooting connectivity to a critical database server named `db1.internal.net`. Standard network utilities produce conflicting IP resolution results as shown below:

text
$ host db1.internal.net
db1.internal.net has address 192.168.1.50

$ dig @10.0.0.53 db1.internal.net +short
10.0.0.150

Which of the following is the most likely cause of this address discrepancy?

  1. A static entry in the local system HOSTS file is overriding standard DNS server resolution.Answer
  2. B
    The authoritative DNS server at 10.0.0.53 is serving stale cached records due to an expired TTL.
  3. C
    Outbound TCP port 53 is blocked by a local host firewall rule on the client workstation.
  4. D
    The DNS server is missing a valid reverse lookup PTR record for host db1.internal.net.

Answer

A static entry in the local system HOSTS file is overriding standard DNS server resolution.
In standard operating system TCP/IP stacks, local name resolution precedence checks local static files (such as `/etc/hosts` on Linux or `hosts` on Windows) before issuing queries to configured DNS servers. When standard lookup utilities yield a different result than an explicit, direct query to the authoritative DNS server, a static mapping in the local HOSTS file is overriding the network DNS response.

Step-by-Step Solution

1
Analyze the output of the default host command
The local system resolver returns IP address 192.168.1.50 when evaluating standard name requests.
The standard system resolver checks local cache and static configuration files before generating external network queries.
2
Analyze the output of the explicit dig command
Bypassing standard OS resolution and querying DNS server 10.0.0.53 directly returns IP address 10.0.0.150.
Explicit dig queries (@server) bypass OS resolution order and directly test the specified server's response.
3
Evaluate standard OS name resolution precedence order
Identify that local HOSTS file entries take precedence over DNS server queries.
Because the DNS server has the correct IP (10.0.0.150) but the system resolves to 192.168.1.50 locally, a local static mapping in `/etc/hosts` (or `C:\Windows\System32\drivers\etc\hosts`) is taking precedence.

Key Concept

Operating System Name Resolution Precedence (HOSTS file vs. DNS Server)
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Topics

Troubleshooting DNS and Name Resolution Services

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