I’ve noticed that I get far more reports from Uptime Robot when
monitoring IPv6 vs IPv4, issues I cannot reproduce when monitoring
myself from other locations. It also sometimes indicates my IPv6 is
still up when it clearly is down; I use a tunnel broker, so if I have no
IPv4 it is impossible for my IPv6 to be up – In some cases when my ISP
is doing maintenance and the modem is completely offline for 30+
minutes, Uptime Robot only catches the IPv4 outage.
In the context of Cloudflare, since Cloudflare offers both IPv4 and
IPv6, Uptime Robot could be checking and tripping on either, or it could
also look like repeated bot type queries to Cloudflare.
Since they do publish a list of IP addresses at
https://uptimerobot.com/locations I have done some local whitelisting,
but I have Uptime Robot configured to monitor my server directly, not
through Cloudflare. Given the number of IPs and the lack of any trivial
way to update the list at Cloudflare, I haven’t bothered to whitelist at