Rapid network development brings challenges to network security and quality of service(QoS). Access control lists (ACLs) are closely related to network security and QoS. By accurately identifying packet flows on a network and working with other technologies, ACLs can control network access behaviors, prevent network attacks, and improve network bandwidth utilization, thereby ensuring network environment security and QoS reliability. This course describes the basic principles and functions of ACLs, types and characteristics of ACLs, basic composition of ACLs, ACL rule ID matching order, usage of wildcards, and ACL configurations.