This document discusses how access control lists (ACLs) can be used to filter network traffic. ACLs allow network administrators to analyze packet contents and either allow or block packets based on criteria like source/destination IP addresses and protocols. ACLs can be implemented on routers, firewalls, and servers to specify allowed traffic, classify traffic for quality of service, and restrict certain activities. The document provides guidance on creating standard, extended, and named ACLs; using wildcard masks; applying ACLs to interfaces; and logging ACL activity for monitoring.