Walk one fault through the seven steps

short · 45 min · Objective 5.1

Task

Take a single injected fault and drive it through CompTIA's seven-step methodology in order, producing the artefact each step is supposed to produce. The goal is not to fix it fast — you already know the cause — it is to feel why each step precedes the next, because the exam tests the order.

Steps

  1. Identify the problem. Gather information before theorising. What fails, for whom, since when, how widely? Establish that Host A reaches other hosts on its own subnet but nothing beyond it, and that Host B is unaffected. Write the scope down — one host, remote-only — because the scope alone eliminates most causes.
  2. Establish a theory. Question the obvious first: link light, interface up, correct IP and mask. Then, because some things work and some do not, reason about the layer. Local works and remote does not points at the gateway.
  3. Test the theory. ip route show and ping -c1 -W2 the configured gateway. The gateway does not answer — theory confirmed. Now turn the card over and confirm you diagnosed the change that was actually made.
  4. Plan the fix and its effects. The fix is to correct the gateway. Note what else it touches: nothing here, but on a shared router the same class of change would affect every host behind it.
  5. Implement. Set the correct gateway (192.168.10.1).
  6. Verify full functionality. Confirm the original symptom is gone — reaching a remote subnet works — and that you broke nothing local.
  7. Document. Record the symptom, the cause, the fix and one lesson learned, while it is fresh.

Verify

ip route show default
ping -c 2 -W 2 192.168.20.10; echo "remote reachable exit $?"
ping -c 2 -W 2 192.168.10.10; echo "local still ok exit $?"

After step six, the remote ping must succeed and the local ping must still succeed — the fix restored what was broken without breaking what worked. The ip route show default line is the one-command confirmation that the gateway is now the real one; before the fix it named an address the second command could not reach.

Notes

The exam does not ask you to fix this fault — it asks what to do next given which step just finished. That is why walking a real fault through the steps in order is worth more than memorising the list: you learn that testing precedes fixing, planning precedes implementing, and that jumping to a plausible fix before the theory is tested is the single most common wrong answer.

Two steps get skipped in real life and are worth over-practising here. Determine if anything has changed is the highest-yield question in troubleshooting, and "nothing changed" usually means "nothing I changed". Document is last and first to be dropped, yet it is the step that turns the next occurrence of this fault from an hour into two minutes.