NetworkingA+

Network Hardware Troubleshooting for CompTIA A+ 220-1101

Network hardware troubleshooting addresses physical layer and device failures that prevent network connectivity. CompTIA A+ 220-1101 tests diagnosing cable issues, NIC failures, wireless signal problems, and router/switch failures. The first rule of network troubleshooting: physical layer first — no software fix can overcome a bad cable or disconnected port.

7 min

2 sections · 7 exam key points

1 practice questions

Physical Layer Troubleshooting

Cable and connection issues: most common network failure. Check: Ethernet cable fully seated (click both ends). LED link light on switch port AND NIC — both must be lit for a physical link. Damaged cable (kinks, crushing, tight bends exceed minimum bend radius). Cable too long (> 100 meters). Use a known-good cable to test. Test the suspect cable with a cable tester. Wrong cable type (crossover vs straight-through — rare issue with Auto-MDIX modern equipment). Check for bent pins in RJ-45 connectors.

NIC (Network Interface Card) failure: link light is on but no connectivity. Symptoms: NIC shows in Device Manager but with yellow warning, 'Network cable unplugged' error even with cable plugged in, no IP assigned. Fixes: update NIC driver. Uninstall and reinstall NIC in Device Manager. Try a different cable. Try a different switch port. If onboard NIC fails — add a PCIe NIC. Disable and re-enable the adapter (Device Manager → right-click adapter → Disable → Enable).

Switch port failure: try a different port on the switch — if a specific port doesn't work but others do, the port is bad. Check switch port LEDs: solid green (link established, no traffic), blinking green (link + traffic), amber/orange (disabled or STP blocking — unusual for unmanaged switches), no light (no link). On managed switches: check if port is administratively shut down.

Wireless Troubleshooting

No Wi-Fi signal: verify the wireless adapter is enabled — check Fn+Wi-Fi key (laptop), Network & Internet settings (Wi-Fi toggle). Check Device Manager — is the Wi-Fi adapter present and without warning? Physical Wi-Fi on/off switch on some laptops. Airplane mode enabled — disables all wireless.

Connected to Wi-Fi but no internet: IP address 169.254.x.x (APIPA) — DHCP failed (router DHCP issue). Wrong password entered — disconnect and reconnect with correct password. DNS failure — test with 'ping 8.8.8.8' by IP (if this works, DNS is broken). ISP outage — check router WAN indicator light or log into router admin page.

Weak signal / intermittent Wi-Fi: move closer to the access point. Interference — 2.4 GHz congestion from neighboring networks, microwaves. Switch to 5 GHz band (faster, less congested, shorter range). Forget and rejoin the network. Update Wi-Fi driver. Check for physical obstructions (concrete walls, metal surfaces block Wi-Fi severely).

Router troubleshooting: reboot the router (power off 30 seconds, power on, wait 2 minutes for full restart). Check router logs for DHCP pool exhaustion (all IPs assigned). Factory reset as last resort — consults manual for reset procedure (usually pin-hole button). Check ISP modem connection — is the modem's internet light green? Call ISP if modem shows no internet connection.

Key exam facts — A+

Physical layer first: check cable, link lights, swap cable before software diagnosis
APIPA (169.254.x.x) on Wi-Fi: DHCP not responding — restart router, check DHCP pool
Connected but no internet: test ping by IP; if it works, DNS is the issue
NIC driver issue: Device Manager yellow warning — update or reinstall driver
Switch port bad: try different port; check port LED (no light = no link)
Wi-Fi interference: change channel on 2.4 GHz (use 1, 6, or 11); or switch to 5 GHz
Router reboot: standard first step for internet connectivity problems

Common exam traps

Restarting the router erases its settings

A power cycle restart (unplug and replug) clears the router's temporary memory and restarts the software — it does NOT erase configuration settings. Settings are stored in non-volatile memory. Only a factory reset (typically via a pin-hole button pressed for 10+ seconds) restores factory defaults and erases custom configuration

Practice questions — Network HW Troubleshooting

These questions are representative of what you will see on A+ exams. The correct answer and explanation are shown immediately below each question.

Q1.A computer connected via Ethernet shows 'Unidentified network — No internet access.' Pinging the default gateway (192.168.1.1) succeeds. Pinging 8.8.8.8 fails. What is the most likely issue?

A.The Ethernet cable is faulty

B.The ISP connection is down or the router's WAN connection has failed

C.The PC's NIC has failed

D.Windows Firewall is blocking all traffic

Explanation: Pinging the default gateway (router LAN IP) succeeds — the local network connection is working perfectly. The failure is only when trying to reach the internet (8.8.8.8). This isolates the problem to the router's WAN (internet) connection — either the ISP is down or the router's connection to the ISP is failed. Check the router admin page for WAN status, check the modem's internet indicator light, and contact the ISP if needed. The Ethernet cable, NIC, and Windows Firewall are all working (local ping succeeds).

Frequently asked questions — Network HW Troubleshooting

What does it mean when a switch port LED is amber/orange?

On most managed switches, an amber/orange port LED indicates: the port is in Spanning Tree Protocol (STP) blocking state — it has detected a loop and is preventing it by blocking traffic on this port. On some switches it indicates a speed mismatch (100 Mbps connection vs Gigabit port). On unmanaged SOHO switches, amber usually indicates a 100 Mbps link while green indicates Gigabit. Consult the specific switch manual for LED color code meanings as they vary by manufacturer and model.

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