Blacklist is a type of access control mechanism, specifically an information security tool, used to control the network access of users and hosts in a computer network. It is a list of IP addresses, hosts, and networks from which no traffic is allowed. Blacklisting is used to prevent malicious actors from gaining unauthorized access to the network, which can be done through malicious IP addresses, as well as to reject or filter out specific types of traffic, such as spam.
The idea behind blacklisting is, to put it simply, to create a list of IP addresses, hosts, or networks that are to be excluded or denied access from the network. This list is used to prevent access from specific sources, such as malicious actors, spam, or intrusive attempts. Blacklisting is commonly employed as an active security measure to temporarily deny access to a particular IP address or range.
Blacklisting can take the form of static or dynamic lists, meaning that they can either be set manually or automatically compiled from outside sources. It can also be applied at various levels, such as by the network administrator, by the ISP (Internet Service Provider), or even on a per-user basis, depending on the security needs of the particular application.
Most of the time, the user or host can specify which IP addresses should be blacklisted, and the blacklisted addresses are stored in a database for easy access. This allows the user to instantly reject unwanted network traffic from specific sources. The benefits of this list-based method of protection are that it is easily enforced, efficient, and relatively secure.
However, the downside of blacklisting is that it is not always effective. Since the blacklists are static, they can be circumvented by malicious actors that know how to exploit them. Blacklisting also requires a certain degree of up-front preparation and effort, so it is not always feasible for larger networks.
