Network Troubleshooting

What this domain actually tests

Nearly a quarter of the exam, and the most scenario-driven domain on it.

CompTIA's troubleshooting methodology, in order — and they test the sequence explicitly:

1. Identify the problem
2. Establish a theory of probable cause
3. Test the theory to determine the cause
4. Establish a plan of action and implement the solution
5. Verify full system functionality and implement preventive measures
6. Document findings, actions, and outcomes

The traps

Documentation is LAST, and verification comes BEFORE it. This is where candidates lose marks that cost nothing to keep. If a question describes a fix that appears to have worked and asks what you do next, the answer is verify full functionality — not "document it and close the ticket."

Get the order wrong and you will confidently pick a wrong answer, because both options look responsible.

Know which tool answers which question:

The symptom-to-cause classics:

• Can reach a site by IP but not by name → DNS.
• Address is 169.254.x.x (APIPA) → the host could not reach a DHCP server.
• Two hosts on the same LAN cannot communicate but each can reach the gateway → check whether they are actually on the same subnet (this is really a subnetting question wearing a troubleshooting costume).
• Intermittent slowness on one link → check for duplex mismatch or a failing cable.

"Why can't host A ping host B?" is the classic frame, and the real question is usually subnet membership or a default gateway. Do the subnetting maths before you theorise about anything more exotic.

How to study it

Memorise the six steps as a sequence you can recite, then practise the "what should the technician do NEXT?" format specifically: read a scenario, identify which step it has reached, name the next one. It is a mechanical drill and it converts directly into marks.

Then learn the tools by the question they answer rather than by what they do. "Where does the path break?" → traceroute. "Is DNS the problem?" → nslookup. That framing is how the exam presents them.

Finally, remember that many troubleshooting questions are subnetting questions in disguise. If a scenario involves two hosts that cannot talk to each other, calculate their subnets before doing anything else.

At 24%, this is roughly 21 questions — the second-largest block on the exam, and one that rewards a memorised sequence more than any amount of networking intuition.