When your website is using some kind of proxy/firewall just like Sucuri to increase the security, you need to make sure that only the allowed ones are accessing the site directly, so that all the requests to the site is going through the firewall.
To ensure this, we use the IP security feature in IIS, in which we can configure which IP’s are allowed.
<system.webServer>
...
<security>
<ipSecurity allowUnlisted="false">
<clear />
<add ipAddress="-.-.-.-" subnetMask="-.-.-.-" allowed="true" />
<add ipAddress="-.-.-.-" subnetMask="-.-.-.-" allowed="true" />
<add ipAddress="-.-.-.-" subnetMask="-.-.-.-" allowed="true" />
<add ipAddress="-.-.-.-" subnetMask="-.-.-.-" allowed="true" />
</ipSecurity>
...
</security>
</system.webServer>In the above code, we set allowUnlisted attribute to false to prevent access to all IP address unless they are listed. And then we add the allowed IP addresses one by one. eg.
<add ipAddress="192.168.134.0" subnetMask="255.255.254.0" allowed="true" />
