What does an Access Control List (ACL) provide for routers and firewalls?

An Access Control List (ACL) primarily provides packet filtering for routers and firewalls. It functions as a mechanism that allows or denies traffic based on predetermined security rules. Each entry within an ACL specifies conditions such as source IP address, destination IP address, or port numbers. When packets traverse a router or firewall, the ACL examines each packet against these rules, determining whether to permit or block the transmission based on the criteria set.

Packet filtering is integral to network security as it enables administrators to control the flow of traffic in and out of the network, thereby providing a layer of protection against unauthorized access and potential threats. ACLs do not inherently perform traffic analysis, redirection, or data encryption; those functionalities require different mechanisms or tools to achieve desired network operations. Hence, the primary functionality attributed to ACLs is their ability to facilitate packet filtering.