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FIELD NOTE 001: REACHABILITY IS NOT APPLICATION HEALTH
Companion to: Ping Works. Your Azure App Doesn't. Here's Why.
Watch: https://youtu.be/NrdW3qekjrU

CONTEXT
A branch employee is trying to reach the company's internal application hosted in Azure. This is an illustrative teaching scenario, not a client incident or a live network trace.

THE KEY DISTINCTION
A successful ping normally demonstrates an ICMP Echo exchange. It does not prove that TCP port 443 is accessible, that TLS negotiation succeeds, or that an application is healthy.

REASONING SEQUENCE
1. Establish who cannot reach what and when the failure occurs.
2. Separate the protocol stages. For this HTTPS-over-TCP example: TCP connection, then TLS, then HTTP.
3. Check the intended destination and service port, the path and return path, and relevant policy. Correlate observations with the actual attempt before changing anything.
4. Ask what each test establishes and what remains untested.

PORTS AND NUANCE
The Short illustrates client source port 51514 and destination port 443. These are logical transport ports, not physical sockets on a device. The animated path is representative, not a measured hop trace.
HTTP/3 uses QUIC over UDP; TCP is not a universal prerequisite for every HTTPS connection.

READ FURTHER
ICMP: https://www.rfc-editor.org/rfc/rfc792
TCP: https://www.rfc-editor.org/rfc/rfc9293
TLS 1.3: https://www.rfc-editor.org/rfc/rfc8446
HTTP/3: https://www.rfc-editor.org/rfc/rfc9114

Practice safely in your own authorized lab. This note is not authorization or a recipe to change production policy.
Prepared November 9, 2026. Reviewed November 11, 2026.