If you want to block a complete IP range in CSF firewall, please follow these steps:
Let’s say you want to block following IP range:
Login in root WHM.
Navigate to: WHM >> Plugins >> ConfigServer Security&Firewall
Block following IP using Quick Deny box.
You may need to restart CSF firewall after adding / removing IPs.
You can also block from SSH using following SSH command:
To block 111.xxx.xxx.xxx range, use following rule
To block 111.111.xxx.xxx range, use following rule
To block 111.111.111.xxx range, use following rule