What its called is 'Rate limiting by IP'.
If you're using Nginx, its provided by the HttpLimmitReqModule. More info here:
http://serverfault.com/questions/179...-prevent-abuse
Basically it lets you make a setting that says no more than X request per second per IP.
If you're using Apache, the module you'd use is called "mod_evasive".
If you're using Lighttpd, the module you'd use is called ModEvasive.
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Using any of those modules may help with your problem, as well as stop people from spidering and ripping your sites quickly. The issue with Google is that if they use many IP addresses, they may get around your rate-limit.