The Switch That Was Not the Problem
A 22-person design studio reports that 'the internet is down'. You arrive and find: the fibre NBN connection box shows a solid green status light; the router's WAN light is green; the main 24-port switch has all port lights dark except the uplink; Wi-Fi appears in the list of available networks but clients get 'no internet'. Two staff on the wired network can reach the office file server but not the internet. A third staff member's laptop works perfectly on Wi-Fi. The studio manager says the cleaner unplugged 'some cables' near the printer on Friday night to vacuum.
1. Diagnose the fault using a layered approach. State what you would test at each layer and what the evidence tells you so far.
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Layer 1 – Physical: the fibre box, router WAN light and one working laptop show the internet service itself is fine. The dark switch ports and the cleaner's unplugging point to a physical cabling fault. Check the patch lead from the router LAN port to the switch uplink, and the patch panel connections near the printer.
Layer 2 – Data link: if the uplink is lit but other ports are dark, the switch may have lost its link to the router or be in a failed state. Check for a loop or a faulty patch lead causing the switch to shut ports down.
Layer 3 – Network: the two wired staff can reach the file server (local subnet works) but not the internet (no gateway/DNS path). That points to the router-to-switch link or the router's LAN interface, not the ISP.
Layer 4+ – Application: the working Wi-Fi laptop proves DNS and internet access are available to at least one device, so the fault is local to the wired path and possibly to the Wi-Fi clients' DHCP lease.
Conclusion so far: the most likely cause is a disrupted uplink or patch-panel connection, not an ISP outage. The evidence rules out the fibre service and the file server.
2. The studio manager wants you to 'just reboot everything now' because a client presentation starts in 30 minutes. Explain how you would sequence the work and what you would say.
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What I would say: 'I can have the wired network checked in about ten minutes. A full reboot of everything will take longer and could lose the configuration if the router is mid-update. Let me reseat the uplink and test one wired machine first; if that doesn't fix it, we reboot the router only.'
Sequence:
- Reseat and test the router-to-switch uplink and the patch leads near the printer - quickest, least disruptive, matches the evidence.
- Test one wired workstation for internet and file server access.
- If still failing, reboot the switch only, then retest.
- Reboot the router last, and only after checking no firmware update is pending.
- Verify Wi-Fi clients obtain a DHCP lease and can browse.
Reasoning: a staged, evidence-led approach preserves the configuration and gets the presentation running sooner than a blanket reboot. A blanket reboot also destroys the fault evidence, making a repeat failure likely. Communicate a realistic time estimate and a fallback (e.g. the working Wi-Fi laptop and a hotspot) so the manager can plan.