ACLs are a set of the most common rules for filtering network traffic. They are used in network devices with packet filtering capabilities (such as routers or firewalls). The ACLs are applied according to the interface of the packets that exit or enter an interface.
For example, on how to use ACLs, consider the following network topology:
Let's say that the S1 server contains some important documents that should be available only to manage the company. We can configure the access list in R1 to allow access to S1 only for network administration users. Any other traffic going to S1 will be blocked. In this way, we can make sure that only the authorized user can access the confidential files in S1.
For example, on how to use ACLs, consider the following network topology: