Diagnose the complete path
Diagnose one complete connection
Trace a browser request from name resolution to the application response and record the first failed boundary.
8 minute lesson
For a final exercise, choose a web service you control. Write down its hostname, expected addresses, transport protocol, port, and URL before testing.
Resolve the hostname. Inspect the route to the chosen address. On the local link, inspect the neighbor entry for the destination or default router. Test the TCP port, then inspect TLS and HTTP with curl -v.
If needed, capture the flow and match packets to each stage: DNS exchange, local frame delivery, routed IP packets, TCP handshake, TLS handshake, HTTP request, and response.
Your result should be one precise sentence, such as: “DNS and routing work, but the server sends a TCP reset because no process listens on port 443.” That sentence is more actionable than “the Internet is down.”
Lesson completed