Suggest an editImprove this articleRefine the answer for “What is ACL?”. Your changes go to moderation before they’re published.Approval requiredContentWhat you’re changing🇺🇸EN🇺🇦UAPreviewTitle (EN)Short answer (EN)**ACL (Access Control List)** is a list of rules that determines which traffic or which users have access to a resource, and which do not. **Key point:** ACL is a basic but very important security mechanism, usually used together with a firewall.Shown above the full answer for quick recall.Answer (EN)Image**ACL (Access Control List)** is a **list of rules** that determines **which traffic or which users have access to a resource, and which do not**. In simple terms: *ACL is a set of "allow / deny" rules.* --- ## Where ACL is used ACL is widely used in networks and systems: - on routers; - on switches; - on firewalls; - in operating systems; - in cloud and corporate networks. --- ## How ACL works An ACL consists of rules that are checked **in order, from top to bottom**. Each rule answers the question of: - **what** (IP, network, port, protocol), - **for whom**, - **allow or deny**. As soon as a rule matches, the check **stops**. At the end there is almost always a rule for: - **implicit deny**, which means "deny everything else." --- ## A simple example ACL is like a guard with a list: - if you are on the list, you go through; - if you are not, entry is denied. --- ## An ACL example on a network (logically) - allow access from the 192.168.1.0/24 network; - deny access from all other networks. --- ## Main types of ACL ### 1. Standard ACL Filters traffic **only by the source IP address**. Simple, but not very flexible. --- ### 2. Extended ACL Filters traffic by: - the source IP address; - the destination IP address; - the protocol (TCP, UDP, ICMP); - ports. **The most common and flexible option.** --- ## What ACL protects ACL helps to: - limit access to networks and services; - segment the network; - reduce the attack surface. ACL is a **basic but very important security mechanism**. --- ## Limitations of ACL It is important to understand: - ACL does not encrypt data; - it does not analyze packet contents; - it does not protect against complex attacks. That is why ACL is usually used **together with a firewall and other defenses**.For the reviewerNote to the moderator (optional)Visible only to the moderator. Helps review go faster.