Access-List (ACL)

Access lists, often abbreviated as ACLs, are lists composed of a series of statements. These statements are used to match specific characteristics of packets or frames. A packet or frame can match an entry, and it will be permitted or denied based on the statement.

We can use ACLs for two main reasons:

• Filtering - where matched packets are either permitted or denied.
• Classification - where matched packets are selected and used for something such as QoS or a VPN.

ACLs operate at layers 2,3, and 4 of the OSI model. For example, they can match on items in all three layers such as IPv4 or IPv6 addresses as well as TCP or UDP ports to match traffic.

Links

https://networklessons.com/security/introduction-to-access-lists-on-cisco-ios-router