Why are inbound ACLs more efficient for the router than outbound ACLs?

Inbound ACLs are more efficient for routers because they filter traffic before it is processed and routed, reducing the load on the router's CPU and memory. By applying rules as packets arrive at the interface, they prevent unnecessary processing of unwanted traffic. In contrast, outbound ACLs require the router to first route the traffic before applying the rules, which can lead to increased resource usage and potential delays. Thus, inbound ACLs help optimize performance by minimizing the amount of traffic that needs to be handled.