Your turn on call
Time to use everything. First you will build the checklist's decision logic as a script, then you will diagnose three real-style tickets from their symptoms alone.
The script takes three findings, in checklist order: the DNS result (ok/fail), the TCP result (ok/fail), and the HTTP status code. It reports the first failing layer with advice, following the rules you know:
- DNS failed → check the name and the resolver (unit 2)
- TCP failed → server down or port blocked (unit 3, lesson 9-1)
- status ≥ 500 → server-side (lesson 4-3)
- status ≥ 400 → client-side, fix the request
- otherwise → healthy
Code exercise · bash
Your turn. Complete the diagnose function: an if/elif chain that checks dns, then tcp, then the status code ranges, printing the exact messages shown in the expected output. Compare strings with = and numbers with -ge.
Problem
Ticket 1: a user's script prints "curl: (6) Could not resolve host: api.internal-shop.com". Which layer of the checklist failed? (One word.)
Problem
Ticket 2: dig +short db.example.com returns an IP, ping to it works, but connecting to port 5432 instantly prints "Connection refused". Naming the checklist layers, which one failed? (One word: the protocol at that layer.)
Problem
Ticket 3: curl -I https://shop.example.com works through DNS, TCP, and TLS, then returns "HTTP/1.1 502 Bad Gateway". Whose side needs the fix, client or server? (One word.)
Quiz
Final check. A page loads fine on your phone's mobile data but fails on the office Wi-Fi with a certificate warning naming the company's "SecureFilter" appliance. What is the most precise description of what is happening?