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practice task

Separate DNS Failure From Server Failure

Users say a site is down, but the server may still be answering. You need to compare public DNS with a forced request to the expected IP.

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Try first

dig +short example.com && curl -I https://example.com/

Goal

Confirm whether the hostname resolution path or the web server response path is failing.

Expected output

DNS should return the public address currently used by clients, and curl should return HTTP headers. A forced --resolve request can prove the target server answers even when DNS points elsewhere.

Teaches

Test name resolution and direct server response separately. A healthy server can still be unreachable through bad DNS.

Common mistake

Treating one successful curl from the server itself as proof that public DNS and external routing are correct.

check your answer

Answer key

What should your command prove?

DNS should return the public address currently used by clients, and curl should return HTTP headers. A forced --resolve request can prove the target server answers even when DNS points elsewhere.

How to explain it

Test name resolution and direct server response separately. A healthy server can still be unreachable through bad DNS.

What to avoid

Treating one successful curl from the server itself as proof that public DNS and external routing are correct.

command set

Commands to know

  1. dig +short example.com
  2. curl -I https://example.com/
  3. curl --resolve example.com:443:203.0.113.10 -I https://example.com/

Related examples

answer check

Compare expected output

Open these command examples to compare your answer against realistic output.

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