What is an Access Control List?

In this article, I will talk about ACL's, what they are, why they are beneficial and how they work.

Let's get started!

What is an ACL?

An ACL (Access Control List) is a set of network traffic filters that can control incoming/outgoing traffic. You can think of it as a "stateless" firewall.

ACL's work on a set of rules that define how to forward or block a packet at the router's interface.
Previously, I have mentioned it is the same as a "stateless" firewall. What do I mean by that? Well, it can only restrict, block or allow packets that are flowing from a source to destination dependent on given rules
When you define an ACL on a routing device, all the traffic flowing through will be compared with the ACL statement, which will either block or allow that packet to be transferred.
ACL's are common in routers or firewalls. But they can also be configured on any device in the network.

The main idea of using an ACL is to provide security to your network.
Without it, any traffic is allowed to enter or exit, making it vulnerable to malicious/unwanted/dangerous traffic.
To improve security, you can deny specific routing updates or provide traffic flow control.

There are two types of Access Control Lists that you can use: Standard and Extended.
Standard ACL allows you to prioritize traffic by the source IP address.
Extended ACL allows you to have greater control of what traffic is prioritizied. It can also use paramaters such as destination IP address, and TCP/UDP ports. This is extremely powerful when implementing security to your network.