Admin->Users and Roles->Banned IPs. Just add one there... use "*" to ban a range.
E.g.
204.236.*.*
Got it, thanks!
How soon the user should be dropped? In other words, does forum drop this user and does it abandon his current session? It's pretty easy to add this functionality. Send me a private email and I will tell the technology. Although sooner or later it will be shared with the source codes anyway... 🙂 I implemented that first in my web app almost 9 years ago.
Dimi