Troubleshooting should identify the first failing layer: resolution, routing, connection, TLS, protocol or application. Each requires different evidence.
Before you start
You should understand clients, servers, IP addresses and ports. Follow a request through name resolution, connection establishment and application exchange. Distinguish protocol guarantees from deployment policy, and use observations from the relevant layer rather than guessing from one browser error message.
The practical goal is to reason through this situation: A DNS success followed by a TLS failure narrows the investigation. Read the walkthrough first, then try the interview exercise before opening its answer. The important part is explaining the decision and its consequences, rather than remembering a definition alone.
Step-by-step walkthrough
Step 1: Record the failed phase
Distinguish DNS, connection, TLS and application errors.
Step 2: Test each boundary
Use observations rather than changing unrelated settings.
Step 3: Compare a known-good path
Differences between networks or clients narrow the cause.
Worked scenario
A DNS success followed by a TLS failure narrows the investigation.
A hostname resolves and TCP connects, but TLS hostname verification fails. This evidence directs investigation toward identity or routing, not SQL queries or DNS availability. If TLS succeeds and the server returns a domain error, application-level context becomes relevant. Preserve timing and resolved addresses alongside the symptom.
Common mistake
Changing application code before checking basic reachability wastes effort.
Verify the behavior
Write down the first failed boundary and the evidence supporting that conclusion.
Interview exercise
Investigate a failed endpoint.
Answer and reasoning
Record the resolved address and timing phases, verify each boundary and compare a known-good client or network.
Continue learning
Compare the scenario with the Networking interview questions and test your understanding with the Networking MCQs. For terminology and implementation details, consult the reference material.