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Difficulty: MediumTroubleshooting DNS and Name Resolution Services

A network administrator is troubleshooting an issue where a user's workstation periodically attempts to connect to an old IP address (10.1.5.50) when reaching `db.internal.corp`, despite the DNS server returning the updated IP address (10.1.5.200) for other hosts. The administrator inspects the client using a local command-line diagnostic tool and views the following output snippet:

text
Record Name . . . . . : db.internal.corp
Record Type . . . . . : 1
Time To Live . . . . : 86400
Data Length . . . . . : 4
Section . . . . . . . : Answer
A (Host) Record . . . : 10.1.5.50

Which of the following actions should the administrator take on the client workstation to resolve this issue and ensure it uses the correct IP address? (Select TWO.)

  1. Execute `ipconfig /flushdns` to purge the local DNS resolver cache.Answer
  2. Inspect the local `hosts` file for static mappings pointing `db.internal.corp` to 10.1.5.50 and remove them.Answer
  3. C
    Run `ipconfig /registerdns` to refresh and clear cached records on the remote DNS server.
  4. D
    Block outbound UDP port 53 traffic on the client firewall to force queries over TCP port 53.

Answer

Purging the DNS resolver cache with `ipconfig /flushdns` and removing any outdated static entry in the local `hosts` file will resolve the issue on the client workstation.
The issue is caused by stale resolution data on the local system. Executing the command to flush the DNS cache clears the local resolver storage so the client sends a new query to the authoritative DNS server. Additionally, checking and editing the local `hosts` file removes any static IP-to-hostname mappings that take precedence over external DNS responses and re-populate the cache upon reboot.

Step-by-Step Solution

1
Analyze the client command output
The `ipconfig /displaydns` snippet reveals a cached A record with a high Time To Live (86400 seconds) mapping `db.internal.corp` to the outdated IP address 10.1.5.50.
When a client system resolves hostnames, it checks the local cache first before contacting DNS servers.
2
Identify the source of stale data and clear the cache
Running `ipconfig /flushdns` purges the local resolver cache so the OS queries the DNS server for fresh resolution.
Local cache entries persist until their TTL expires unless manually flushed.
3
Check persistent local overrides
Examining the local `hosts` file ensures that static mappings overriding DNS responses are identified and removed.
Static `hosts` entries take precedence over DNS server queries during local resolution.

Key Concept

Local Resolver Cache and Hosts File Precedence in DNS Name Resolution
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Topics

Troubleshooting DNS and Name Resolution Services

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