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Difficulty: HardTroubleshooting DNS and Name Resolution Services

A network technician is systematically troubleshooting a Linux workstation that fails to resolve an internal fully qualified domain name (FQDN). Arrange the following diagnostic steps in the correct order, starting from local client configuration inspection and escalating through to upstream network infrastructure isolation.

  1. 1Inspect the local `/etc/hosts` file to verify no static mapping exists that overrides DNS name resolution.
  2. 2Examine `/etc/resolv.conf` to ensure the workstation is configured with the correct IP address for the local recursive DNS server.
  3. 3Flush the local DNS resolver cache using `resolvectl flush-caches` to clear potential stale resource records.
  4. 4Execute `dig @<Internal_DNS_IP> <FQDN>` to test direct DNS query and response behavior with the configured internal DNS server.
  5. 5Execute `dig @8.8.8.8 <FQDN>` to determine if the name resolution failure is restricted to internal DNS or affects external connectivity.

Answer

The correct sequence starts with inspecting the local hosts file, followed by checking local resolver IP configuration in `/etc/resolv.conf`, clearing local resolver cache, querying the targeted internal DNS server directly via `dig`, and finally querying an external public DNS server to isolate internal vs. external scope.
Systematic network troubleshooting follows a bottom-up / local-to-remote sequence: first checking local static files (`/etc/hosts`), then local network client configuration (`/etc/resolv.conf`), followed by local cache clearing (`resolvectl flush-caches`), then testing targeted internal DNS server responses via direct `dig` queries, and lastly testing external DNS reachability to isolate enterprise boundary issues.

Step-by-Step Solution

1
Check local static mappings in `/etc/hosts`.
Ensures no hardcoded IP address or hostname entry is overriding standard DNS queries on the endpoint.
The OS checks local host files prior to making network resolver requests.
2
Verify client DNS server IP settings in `/etc/resolv.conf`.
Confirms the workstation attempts DNS queries against valid, reachable DNS IP addresses.
If the configured DNS server IP is incorrect or misassigned by DHCP, network queries will fail regardless of server status.
3
Clear cached name resolution entries using `resolvectl flush-caches`.
Purges temporary cached lookup failures or expired record mappings.
Eliminates local cache corruption or stale TTL records as the root cause.
4
Directly query the internal DNS server using `dig @<Internal_DNS_IP> <FQDN>`.
Determines if the internal DNS daemon responds on UDP/TCP port 53 and returns valid resource records.
Isolates the local resolver library from the actual network response of the designated DNS server.
5
Query a public external DNS resolver using `dig @8.8.8.8 <FQDN>`.
Helps distinguish between an isolated internal DNS server issue and broader firewall or outbound network connectivity failures.
Determines if DNS traffic generally egresses the host and isolates internal infrastructure misconfigurations.

Key Concept

Systematic DNS Troubleshooting Sequence
Estimated Time:2m 0s
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Topics

Troubleshooting DNS and Name Resolution Services

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