Dynamic IP Restrictions for IIS allows you to reduce the probabilities of your Web Server being subject to a Denial of Service attack by inspecting the source IP of the requests and identifying patterns that could signal an attack. When an attack pattern is detected, the module will place the offending IP in a temporary deny list and will avoid responding to the requests for a predetermined amount of time.
The Dynamic IP Restrictions Extension for IIS provides IT Professionals and Hosters a configurable module that helps mitigate or block Denial of Service Attacks or cracking of passwords through Brute-force by temporarily blocking Internet Protocol (IP) addresses of HTTP clients who follow a pattern that could be conducive to one of such attacks. This module can be configured such that the analysis and blocking could be done at the Web Server or the Web Site level.
Microsoft document which eplains some deatils and you can dowmload this module