NACL vs Security Groups: What Are the Differences?


Security groups and Network Access Control List (NACL) are two major components of an organisation’s network security. These security parameters are kind of similar and act as virtual firewalls protecting the network. The most significant similarity is that both NACL and Security Groups use inbound and outbound rules to control the traffic to and from the resources within a VPC (Virtual Private Cloud).

However, both technologies have some distinctions. Read on to learn more about NACL vs Security Group and the subtle differences that set the two apart. To enhance your knowledge in network security, register for the Master of Science in Computer Science from LJMU.

Network Security in Cloud Computing

Network security in cloud computing refers to the various technologies, processes, controls and policies used to protect data and enhance data security. Its sole focus is to protect cloud networks from unauthorised access, misuse, modification or data exposure. It helps maintain confidentiality, integrity and availability of data. 

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Understanding Amazon Web Services

Amazon Web Services (AWS) is an online platform that provides easy and cost-effective cloud computing solutions. It offers many advantages and accessible services such as data storage, first content delivery, computing power, etc. It helps companies scale heights and grow their operations to meet market demands.

What Are NACLs?

Network Access Control Lists is a firewall to your network that protects your system and is an operational layer of security that protects the VPC for controlling traffic within the network. NACL provides an additional layer of security to Amazon Web Services. 

It secures the VPC that can be imagined as containers for storing subnets. Hence, it helps to manage and control traffic efficiently and provides data storage security.

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Advantages of NACL Over Security Groups

Organisations can improve network security, reduce risks, and ensure that only authorised users can access the network by implementing access control. The following are some advantages of NACL over Security Groups:

  • Takes charge of the resource access system
  • Manages user and device network access orchestration
  • Easily identify suspicious activities within the network
  • Adds the user segmentation feature based on roles
  • Provides the discretion to accept or reject guest networks
  • Enables incident response automation
  • Enhances the regulatory compliance system

Disadvantages of NACL Over Security Groups

Understanding the pros and cons of each technology helps make the ultimate choice in the Network ACL vs Security Group debate. The disadvantages of NACL over Security Groups are enumerated as follows:

  • Challenging to determine the access rights of a given subject
  • Difficult to remove a user’s rights from all objects

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How NACLs Work

To understand the concept of AWS NACL vs Security Group, it is crucial to understand how each works. Network ACLs work according to the following rules:

  • Rule number: The rule with the lowest number is examined first. A rule with a higher number can also be given a green signal if it is compatible with the traffic at that time.
  • Type: The type of traffic can be specified or customised within the range.
  • Protocol: The protocol must be specified with any standard number. One can choose whether they want to specify all or some of the numbers.
  • Port range: The traffic must be within the specified port range. For instance, 80 is the port range for HTTP traffic.
  • Destination: The outbound rules must be followed to reach the destination within the network.
  • Allow/Deny: Lastly, it depends upon the network controller whether they want to allow or deny the traffic.

What Are Security Groups?

Security Groups control the incoming and outgoing traffic to Amazon Web Services, acting as a virtual firewall that helps control the traffic flow. The various internal and external rules control the flow. The concept of Security Groups is a milestone in understanding the difference between NACL and Security Groups.

When a Security Group is created, it is assigned to a particular VPC. Each group is given a name and description to find them easily whenever required. 

Advantages of Security Groups Over NACLs

The role of Security Groups in protecting a network and their various advantages are stated below:

  • It functions at the instant level without making any delays.
  • It allows return traffic regardless of the rules.
  • It automatically allows the response traffic.
  • Assists in securing the cloud environment.
  • It is in charge of the traffic allowed to the EC2 machines.

Disadvantages of Security Groups Over NACLs

Although Security Groups have proven helpful in many ways, they are not devoid of drawbacks. The disadvantages of Security Groups over network ACL are enumerated as follows:

  • Security Groups have a maximum inbound and outbound rule of 60.
  • It has to be explicitly assigned to a particular instance.
  • It can only allow traffic and does not support ‘deny’ rules.

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How Do Security Groups Work?

A Security Group is installed to control the traffic allowed to leave or reach the associated resources. For instance, it controls all the inbound and outbound traffic when connected to an EC2 machine. There is a difference between NACL and Security Groups and how they work. 

However, Security Groups can be associated only with the particular resources in a VPC for which it has been created. When VPC is created, it comes with a Security Group by default. Following this, particular Security Groups can be created for each VPC. 

The availability zone of a VPC is installed with a public subnet for web servers and a private subnet for database servers. Load balancers are equipped with separate Security Groups that help to allow HTTP and HTTPS traffic within the network.

Differences Between NACLs and Security Groups

The difference between Security Group and NACL is broadly classified as follows:

NACL Security Groups
Network ACLs operate in subnet levels Security groups function at an instance level
It supports both ‘allow’ and ‘deny’ rules. It only supports ‘allow’ rules.
It should explicitly allow the return traffic and is, therefore, stateless. It is stateful because of the creation of inbound and outbound rules.
NACL supports the blocking of specific IP addresses if found suspicious It cannot block specific IP addresses
The rules are processed as per number order while alloying the traffic The rules are entirely processed before deciding to allow the traffic.
It automatically applies all instances with subnets without the interference of the user It applies when a user specifies a Security Group when launching an instance and associates it with the Security Group.

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Use Cases of NACLs

NACL is widely used in organisations today, as discussed below:

  • It is generally used in promoting safe collaboration with major industry giants and corporate partners. It helps to avoid network jargon in big firms and offices.
  • Network ACLs are extensively used in case of incidence response. In times of cyberattacks, NACL springs into action to protect the network from potential threats.
  • It is also a great way of handling IoT-based systems. IoT is a powerful tool for organisations in various sectors, and network ACLs are connected to IoT devices to monitor traffic flow.
  • NACL is essential for maintaining security compliance with relevant cybersecurity regulations and standards.

Use Cases of Security Groups

The everyday use cases of Security Groups are enumerated as follows:

  • It is widely used to connect to a Linux CVM remotely through SSH.
  • It is used to connect to a Windows CVM remotely via RDP.
  • It is also used to test the communication power of the CVM with other CVMs on the internet.
  • Security Groups are used in organisations to log in to a CVM via Telnet.
  • It provides access to a CVM to any particular external IP address.

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Choosing Between NACLs and Security Groups

When it comes to Network ACLs, the rules are applied to their priority, where the priority of each rule is demonstrated with a particular number. However, when Security Groups are concerned, all the rules are applied to an instance. There is no point in choosing any rule to apply to an instance. This implies that each rule is assessed according to its priority.

Thus, in the race of NACL vs Security Group, NACL takes the upper hand in some cases, whereas Security Groups are applicable in others. It entirely depends upon the need, functionality, and type of the network.

Security Best Practices With NACLs and Security Groups

Some of the best practices with Network ACLs and Security Groups are:

  • Reduce the size of the source and destination traffic in Network ACL rules whenever possible.
  • Keep the NACL as simple as possible and use them judiciously to deny traffic.
  • Use NACLs mindfully, deploying them per the purpose of the subnet to which they are connected.
  • Avoid using the default Security Group and customise the Security Groups as per your requirement.
  • The number of Security Groups must be preferably restricted to a minimum.


NACL and Security Groups are vital for protecting and working with networks. Companies today employ professionals with a deep understanding of NACL and Security Groups and the necessary knowledge to work with these technologies. 

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Frequently Asked Questions

What is the difference between default NACL and default Security Group?

Security Groups are locked down by default, whereas NACL must have a subnet by default. The NACL is configured to allow or deny the traffic in and out of the network.

Does NACL override Security Groups?

Network ACLs are applicable at the subnet level, whereas Security Groups are applicable at an instance level. So any instance in a subnet will follow the NACL rules. In the case of Security Groups, it has to be explicitly assigned to an instance, meaning any instance within the subnet will get the rule applied.

Can we block an IP address in NACL?

Hackers don't use a single IP address to perform malicious attacks. They jump from one IP address to another in the process. Hence, blocking a suspicious IP address or range using Network ACL is difficult.

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