I think the IP Blocker page on Moodle needs some enhancement / improvements.
I had added about 14 CIDR networks to the blocked IP list previously and this seemed to work OK (prevented new Moodle accounts from being created by spammers).
Upon investigating why another school district could not seem to access our Moodle server through a parent-child proxy server configuration, I added the RFC1918 private address space to the addresses (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16) to the Allowed IP List, without realizing that any addresses outside of those specified would be blocked from accessing Moodle. I locked myself out of the server from home, and had to drive back to the office late at night to fix my mistake!
There should be some warning on the Moodle IP Blocker page to indicate this, as there minimal instructions to be found on the IP Blocker page.