Define the scope of the map
This map describes HTTPS using HTTP/1.1 or HTTP/2 when a new connection is required. Browsers may cache DNS or reuse connections; HTTP/3 uses QUIC instead of TCP. The map explains responsibilities rather than a fixed sequence repeated on every click.
A URL’s hostname helps locate a destination, while its path identifies a resource on that service. In https://docs.example.test/guide/, docs.example.test is the host and /guide/ is the path. They answer different questions.
Further reading: MDN: Overview of HTTP
What the four layers provide
DNS obtains resource records for a name. TCP provides reliable byte transport in this scenario. TLS negotiates protected communication and verifies appropriate peer identity. HTTP expresses methods, paths, status and content. DNS success does not guarantee TCP reachability, and TCP success does not establish application authorization.
Each layer has its own failures. A nonexistent name, connection timeout, certificate mismatch and HTTP 404 are different evidence. Calling all of them “the network is broken” makes the next step ambiguous.
Further reading: RFC 1034: Domain names, concepts and facilities·MDN: Transport Layer Security·MDN: Overview of HTTP
Start with the nearest failure evidence
Receiving HTTP 404 means an HTTP service responded to that request. First check the host, path and routing configuration. It does not guarantee the expected origin produced the response, particularly when proxies or caches are involved.
If the browser shows a certificate security warning, check identity, time and configuration with the responsible owner instead of bypassing the warning to finish a test. Diagnosis should establish a verifiable cause while preserving the security boundary.
Example: a 404 points first to the path
A synthetic trace shows DNS resolved, TCP connected, TLS verified and GET /guied/ → 404. The intended path is /guide/.
An HTTP response makes spelling and routing a more direct next check than assuming complete DNS failure. After correcting it, obtain the expected response before claiming a fix.
Conclusion: Correct the observed path typo, then verify status and content.
Offline exercise: next checks for three errors
Use synthetic text traces without sending network requests or changing DNS.
- List A: name not found, B: certificate mismatch and C: HTTP 404.
- For each, name the relevant layer and one next check.
- For C, add one unsupported conclusion, such as “the entire domain does not exist.”
Expected result
For A, check the name and DNS. For B, check certificate identity and configuration without bypassing warnings. For C, check host, path and routing.
Check your work
If the connection uses HTTP/3, which transport protocol label changes?
Finish and clean up
Save the layered notes; no network settings require restoration.