"Connectivity testing on TP-Link Wi‑Fi extenders" NTP server misuse and abuse - Wikipedia https://en.wikipedia.org/wiki/NTP_server_misuse_and_abuse#Connectivity_testing_on_TP-Link_Wi%E2%80%91Fi_extenders

> Firmware for TP-Link Wi‑Fi extenders in 2016 and 2017 hardcoded five NTP servers, including Fukuoka University in Japan and the Australia and New Zealand NTP server pools, and would repeatedly issue one NTP request and five DNS requests every five seconds consuming 0.72 GB per month per device.[20] The excessive requests were misused to power an Internet connectivity check that displayed the device's connectivity status in their web administration interface.[20]

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ところで一つのWikipedia記事になるぐらいにはNTPサーバー誤用・悪用されてるんだってなってる