AI Network Labs 08 — Lab: Break–Fix Troubleshooting
Let the AI break a working network, then diagnose it bottom-up with getNetwork, getDeviceInfo, show commands and getCommandLog — without guessing.
Building is the easy half. This lab flips it: a partner (or the AI) breaks a working network, and you use the inspection tools to find the fault — without guessing and without rebuilding.
The method: bottom-up, one layer at a time
| Layer | Question | Tool / command |
|---|---|---|
| 1 · Physical | Is there a cable, and is the device powered? | getNetwork, getDeviceInfo, setPower |
| 2 · Data link | Is the port up, in the right VLAN, trunking? | show interfaces status, show vlan brief, show interfaces trunk |
| 3 · Network | Right address, mask, gateway? A route back? | getDeviceInfo (PC), show ip interface brief, show ip route |
| 4+ · Policy | Is an ACL dropping it? | show access-lists |
| History | What changed? | getCommandLog |
getCommandLog is the troubleshooter's cheat code. In a real network you'd compare against a config backup; here Packet Tracer already kept one.
Set up the break
Start from the finished VLAN lab and ask the AI to break it — without telling you how:
Introduce exactly ONE fault into this network that stops PC-S1 reaching PC-E1.
Do not tell me what you changed. Do not use getCommandLog afterwards.Diagnose with a constrained prompt
PC-S1 cannot reach PC-E1. Diagnose it bottom-up:
1. getNetwork — confirm cabling and power.
2. getDeviceInfo on both PCs — address, mask, gateway.
3. On SW1 and R1 run: show vlan brief, show interfaces trunk, show ip interface brief.
At each step, state what you expected, what you saw, and whether this layer is healthy.
Do NOT change any configuration until you name the fault.Five classic faults to practise
| Fault | Where it shows up |
|---|---|
Subinterface shutdown on the physical port | show ip interface brief: Gi0/0 administratively down |
Wrong encapsulation dot1Q VLAN number | Subinterface up/up, but no replies — compare with show vlan brief |
VLAN missing from switchport trunk allowed vlan | show interfaces trunk — VLAN absent from "allowed and active" |
| PC gateway typo (.10.254 instead of .10.1) | getDeviceInfo on the PC |
ACL without a final permit ip any any | show access-lists — only deny counters increase |
Close the loop
After the fix, re-run sendPdu + getPduResults, then — and only then — open getCommandLog to check your diagnosis against what really changed.
Exercise
Write your own "fault card" for each of the five faults: symptom, the single command that reveals it, and the fix. That card set is worth more in an exam than any number of rebuilt labs.
ExerciseKnowledge check
In the bottom-up method, what do you check before IP addressing?
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