I find on the latest version of the software the IP address range does NOT work.
I setup the rule:
IP Range: Block visitors with IP addresses in the range: 188.8.131.52 - 184.108.40.206
Someone in that range keeps trying to log in.
When I go and look it says "0 blocked hits".
I am able to manually block the ip address and then make it permanent but would rather just block the whole range...