How the diagnostics work

Four pages on what the numbers actually measure. If you only read one, read the first.

What a browser cannot doMixed content, the CORS-safelisted response headers, opaque responses, and why ping is an HTTPS round trip.

DNS over HTTPSWhat DoH gives you, what it does not, and why the DNSSEC indicator is a resolver's claim.

Desktop-only capabilitiesICMP, traceroute, TCP connect scanning and ARP, and how each is actually implemented.

Address math, walked throughRFC 5952 compression, modified EUI-64, solicited-node multicast and MTU overhead, with worked numbers.