Read IPv4 and subnetting.
Client configuration and connectivity checks
Start with your own device: does it have the intended address, prefix, gateway and DNS server? On Windows use ipconfig /all. On many Linux systems use ip address and ip route. On macOS use ifconfig and route -n get default. Command availability and interface names vary.
Ping your gateway, then a known permitted remote IP. Use nslookup example.com to ask a DNS question. A failed ping can mean filtering as well as a broken path. tracert on Windows or traceroute on many Unix systems explores hops; an asterisk can mean the device did not reply, not necessarily that forwarding stopped.
Distinguish DNS failures from connectivity failures
If a service works by IP but not by name, inspect DNS. If the name resolves, check the application port and service. A browser can still reject a certificate when you enter an IP directly, so compare the right kind of evidence. HTTPS uses encryption and server identity checks; it does not guarantee that a site’s content is trustworthy.
Only run connectivity tests against systems you own or have permission to test. Record actual output with your operating system and date. Avoid publishing public addresses or identifying information from work networks.
Verification commands
Use these viewing commands to inspect the idea in this lesson. Start in the environment shown above each example.
ipconfig /all
nslookup example.comCommand reference · enter in the stated environment; output varies by device.
ip address
ip routeCommand reference · enter in the stated environment; output varies by device.
ifconfig
route -n get defaultCommand reference · enter in the stated environment; output varies by device.
Practical exercise
Write a troubleshooting sequence for “my laptop cannot open the school website”. Start locally, then move outward.
Show the answer and explanation
Check link/Wi-Fi association, local IP settings, gateway reachability, routing, DNS resolution, and the requested application/port. Compare with another device and record which step first differs from expected behaviour.
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Technical references checked on 25 October 2026. These are original teaching explanations, not official Cisco course material. See how content and lab validation are described.
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