How we measure this — two independent signals, we don't actively ping every network on a fixed schedule:

Responsive-host snapshot — every IP below answered ICMP in our last internet-wide sweep. A periodic, one-pass census — not continuous monitoring.

Reachability trend (chart) — accrues passively from real user checks: each day counts the distinct hosts in this AS that responded to a ping someone actually ran. A sustained drop can flag an outage or new filtering.