An ACL is essentially a packet filter. An ACL takes effect only after it is applied to a service module.

The statement is correct. An Access Control List (ACL) is a fundamental network security tool used to define a set of rules for filtering network traffic. It functions as a packet filter by inspecting packets against these rules and then permitting or denying them. However, simply creating an ACL on a device does not activate it. The ACL must be explicitly applied to a specific location, such as a network interface (in a specific direction, inbound or outbound) or a service module (like VTY lines for remote access control), for its rules to be evaluated against traffic.

This is a True/False question, so there is no "incorrect option" other than the "False" choice. The statement would be false if an ACL could take effect without being applied, or if its primary function was not packet filtering, neither of which is true.

1. Huawei Enterprise Networking Documentation. (2019). VRP V800R012C10 Product Documentation - ACL Configuration. Section: "ACL Overview". "An access control list (ACL) is a list of rules that classify packets... After rules are defined, the ACL must be applied to a specific object to take effect."

2. Huawei Enterprise Networking Documentation. (2019). VRP V800R012C10 Product Documentation - ACL Configuration. Section: "Applying an ACL to a Traffic Policy". "After an ACL is created, you need to apply it to a traffic policy to filter packets."