If you would like to block an IP address from accessing your website you can do so via the web.config file in your websites wwwroot.
Place the following code within the <system.webServer> tags in the web.config file:
<security>
	<!-- line allows everyone, except below IP-->
	<ipSecurity allowUnlisted="true">
		<clear/>
		<!-- blocks the specific IP -->
		<add ipAddress="xx.xx.xx.xx"/>
	</ipSecurity>
</security>replacing xx.xx.xx.xx with the valid IP address.
