Final answer:
An access control list (ACL) is a network security measure that permits or denies traffic through a router based on specific criteria, functioning similarly to selective permeability in barriers.
Step-by-step explanation:
An access control list (ACL) permits or denies traffic through a router based on specific defined criteria. This concept is similar to the selective permeability feature of any barrier that allows certain substances to cross but excludes others. ACLs are used in networking to provide a layer of security by controlling the flow of network traffic. A well-configured ACL can protect a network from unauthorized access, while still allowing necessary communication between devices.
Access control lists are made up of a series of rules, or entries. Each rule specifies certain conditions such as source and destination IP addresses, protocol type, and port number. When a packet arrives at a router, the ACL rules are evaluated in a sequential order to determine if the packet should be allowed through or blocked. It's essential in network administration to set these rules carefully to ensure that legitimate traffic is not inadvertently blocked while maintaining network security.