Lesson 5: Service and Wi-Fi Failure Challenge

Core path: 42 minutes

Five users can all say "Wi-Fi is broken" while describing five different failures.

Your job is to separate them.

Ticket A: connected, APIPA address

Evidence:

• client associates to SSID;
• signal is strong;
• IPv4 is 169.254.18.42;
• expected DHCP configuration is absent.

Focus on DHCP/configuration path, not radio strength.

Ticket B: remote IP works, hostname fails

Evidence:

• valid address and gateway;
• remote documentation IP responds;
• portal.test does not resolve.

Focus on DNS.

Ticket C: strong signal, no network path

Evidence:

• client associates;
• AP signal is strong;
• AP uplink to switch is disconnected.

A strong radio link does not prove the AP has a usable wired/upstream path.

Ticket D: service on wrong port

Evidence:

• hostname resolves;
• host is reachable;
• documented service expects TCP 443;
• application is listening on another configured port.

Focus on service/listener configuration.

Ticket E: crowded 2.4 GHz room

Evidence:

• wired clients are healthy;
• wireless clients near the AP associate successfully;
• latency/throughput degrade as the room fills;
• channel analysis shows heavy overlap/congestion.

Focus on radio capacity/interference before DNS.

Incident record

Choose three tickets and document:

symptom:
what still works:
first failed/unproven boundary:
strongest theory:
alternative theory:
one controlled test:
expected result:
verification:

Week 8 defense

Explain why each of these statements is wrong:

• "Strong Wi-Fi bars mean the internet works."
• "A private IP address means the network is secure."
• "DNS and DHCP are basically the same thing."
• "443 means every HTTPS implementation must always use only TCP."
• "NAT is the firewall."

The goal is not to memorize networking trivia. It is to know which mechanism to test next.