NETWORK NOTES

When a website will not open

1. Establish the scope

Open another known website. If only one destination fails, record its exact address and error. Check the device clock because an incorrect date can cause certificate errors.

2. Check name resolution

nslookup example.com

An answer means the name resolved, not that the service is healthy. Compare IPv4 and IPv6 records when results differ between networks.

3. Check the application response

curl --head --max-time 10 https://example.com

A redirect or HTTP error still indicates that an HTTP response was received. Preserve the status code. Do not add options that disable certificate verification.

4. Compare another network

Repeat on mobile data or another connection. A different result narrows the scope but does not alone identify the cause.