Router and Routing Basics - Access Control List

ACLs are lists of conditions that are applied to traffic traveling across a router's interface.  These lists tell the router what types of packets to accept or deny. Acceptance and denial can be based on specified conditions. ACLs enable management of traffic and secure access to and from a network.
ACLs can be created for all routed network protocols, such as Internet Protocol (IP) and Internetwork Packet Exchange (IPX). ACLs can be configured at the router to control access to a network or subnet.