What is an Access Control List?

Before granting access to any areas of your network or devices, it’s important to first compile a list of authorized personnel and resources into what’s called an access control list (ACL).

The ACL by definition is a…list…of designated users or systems that have access to specific objects or resources.

A network is a lot like a country club. In order to become a member, you have to meet certain requirements. For example, you might have to pay dues and be sponsored by another member. Once you’ve met the requirements, you can visit the club whenever you want.

By asking the following questions, those responsible for the security of their networks and devices can start to design a list of authorized personnel and resources for each area of their assets.

  1. Who is responsible for security on your network and devices?
  2. What resources and personnel are authorized in each area of your assets?

The Different Kinds of ACLs

There are two basic kinds of ACLs:

  • Filesystem ACL: is like a security guard for your computer, managing access to directories or files. A filesystem ACL tells the operating system which users are allowed to access the system, and what privileges they have once they’re inside.
  • Networking ACLs: are an important tool for managing access to a network. By providing instructions to switches and routers about the types of traffic that are allowed to interface with the network, they help ensure that only authorized users and devices can gain access.

But wait…there’s more!

There are five types of ACLs that you can use for different purposes are:

  • Standard
  • Extended
  • Dynamic
  • Reflexive
  • Time-based ACLs

We’ll go into what each type of list is later.

The Pros/Cons of an Access Control List

There are a variety of security controls that can be implemented using access control lists. However, it is important to weigh the advantages and disadvantages of using an ACL before deciding if it is the right choice for your particular situation.

A well-configured ACL can play an important role in protecting your network from common attacks. An ACL can help to restrict the number of users and traffic that a router is aware of. By creating a list of rules, an ACL tells the router which types of traffic should be allowed on each interface.


The main strength of ACLs is their simpilicity. By clearly displaying the levels of access and permissions that each user, group, or device has on a particular system, it is easy to understand and manage an ACL. This makes it simple for administrators to control who can access what parts of the system, and to revoke permissions as needed.


ACLs have several disadvantages that users should be aware of before implementing them. These disadvantages include inefficiency, a lack of scalability, and a lack of visibility.

In an ACL system, permissions and access are determined by explicit declarations, rather than being inferred from membership in groups. This can be inefficient, for example, if a user has unique access or permissions because they are both in the IT department and a manager. In these cases, all the necessary information must be stated explicitly, rather than being implied by the user’s membership in multiple groups. This requirement for an explicit declaration of access controls also impacts scalability.

As the number of users, groups, and resources continues to increase, so does the length of the ACL and the time required to determine the level of access granted to a particular user. This can become quite cumbersome and difficult to manage effectively.

Organizations using ACLs to manage permissions and levels of access for users may find it difficult to audit, change, or revoke access when needed. This is because a user’s permissions and levels of access can be scattered across multiple, standalone lists.

ACL Implementation: Is it Easy?



Time consuming?


Worth as another form of protection against unauthorized access to networks and devices?


ACLs: Protect Your Network Like an Exclusive Club

An ACL can be a helpful means of controlling access to sensitive information within a private network.

By placing an ACL at various points throughout the network, administrators can install rules that prevent unauthorized users from accessing shared data. While it is better suited to high-speed and high-performance networks, an ACL can be implemented by network administrators working at any level.

ACLs are well worth the time and effort to master. Having such a versatile tool in one’s toolkit is a great advantage for network administrators.

However, as with most security topics, there isn’t just one solution to ACLs. Careful research of deployment options for each network that is designed, taking into consideration all of the security threats as well as cost and performance should be factors on which ACL to us.

Protect those networks and devices like they are important to your organization…because they are.