block registarion with specific IP

hello, your plugin is exactly what i was looking for thanks!
just one question please –
when I see the ip
what/how should be the step to prevent this IP from creating anthor new account?
should i need another plugin for that?
if i do, can u please recommend me?
(i have a very high traffic site. so something that would not cause slowing down my site)
your answer will be great appreciated!