4.3.1. Troubleshooting Wired and Wireless Network Issues

💡 First Principle: Use command-line tools (ipconfig, ping, tracert) to quickly test and verify different layers of network connectivity, from local IP configuration to routing paths.

Scenario: A user reports "no internet." You sit at their computer to begin troubleshooting.

Technician's Diagnostic Path:

1. Check Local IP Configuration:
   • Action: Open a command prompt and type ipconfig (Windows) or ifconfig (Linux/macOS).
   • Analysis: Do they have an IP address? Is it an APIPA address (169.254.x.x)? If so, they can't reach the DHCP server. Is the Default Gateway correct?
2. Test Local Network Connectivity:
   • Action: ping <default_gateway_IP>. For example, ping 192.168.1.1.
   • Analysis: If this works, their local connection to the router is good. The problem is likely beyond the router.
3. Test Internet Connectivity:
   • Action: ping 8.8.8.8 (a public Google DNS server).
   • Analysis: If this works but browsing doesn't, the problem is almost certainly DNS. If this fails, the problem is with the router's connection to the internet or the ISP.
4. Test DNS Resolution:
   • Action: nslookup www.comptia.org.
   • Analysis: If this fails but ping 8.8.8.8 worked, the configured DNS server is down or incorrect.

⚠️ Common Pitfall: Assuming a "no internet" problem is an ISP outage. It is far more likely to be a local issue with the user's computer, a cable, the local switch, or the SOHO router.

Key Trade-Offs:

• Wired vs. Wireless Troubleshooting: Wireless adds layers of complexity like signal strength, interference, and encryption that are not present in wired troubleshooting.

Reflection Question: You are troubleshooting a "no internet" issue. You use ipconfig and see the user has an IP address of 169.254.10.20. What does this tell you, and what is your next troubleshooting step?