It turns out that Postgres has CIDR-arithmetic functions. I was ignoring that stuff because it's a pain in the ass. It turns out that it isn't a pain in the ass because Postgres has builtin support for it.

For example, you can see all of the Lemmy instances hosted behind Cloudflare here: https://fedilist.com/instance?q=&ip=104.16.0.0%2F12&software=lemmy®istrations=&onion=

Or just all the instances behind Cloudflare: https://fedilist.com/instance?ip=104.16.0.0%2F12

Some of the network-based info is available under the "Crawling Info" section. If you check https://fedilist.com/instance/fsebugoutzone.org , you can see "CIDR: 216.126.224.0/20";, and that link is clickable and goes to https://fedilist.com/instance?sort=discovered&ip=216.126.224.0/20 , which shows FSE's neighbors. Apparently, we're on the same /20 as @Cocoa Cocoa Hoto (real) 's instance, and a few others. Two Jesus-themed Peertube instances, for example.

Also the live view is still entertaining: https://fedilist.com/ttyd/
disable_ipv6.jpg