Network security is a crucial element of any network strategy. Cisco routers can be used as part of your
network security strategy. The most important tool in Cisco IOS software used as part of that strategy are
Access Control Lists (ACLs). ACLs define rules that can be used to prevent some packets from flowing
through the network and should be part of an organization's security policy.
IP access control lists (ACLs) cause a router to discard some packets based on criteria the network engineer
defines by means of filters. The goal of these filters is to prevent unwanted traffic in the network. Access
lists.
There are two main categories of IOS IP ACLs:
• Standard ACLs, which use simpler logic; and
• Extended ACLs, which use more-complex logic.