IP blacklisting is a method used to filter out illegitimate or malicious IP addresses from accessing your networks.
Blacklists are lists containing ranges of or individual IP addresses that you want to block. Although blacklisting is a good way to prevent specific IPs from accessing your network, it is not a foolproof method.
Creating and applying blacklists enables you to filter malicious traffic according to policies or through the manual addition of IP addresses. Many network security tools that use blacklists are also able to add new addresses to be blocked. This can be done as externally referenced lists are updated or according to the results of event analysis.