AWS Security Group vs NACL

AWS Security Group vs NACL: What’s the Difference?

When working with AWS infrastructure, controlling inbound and outbound traffic is essential for security. AWS provides two core components to manage this: Security Groups and Network Access Control Lists (NACLs). Although they serve similar purposes, their roles, scope, and behavior differ significantly. In this post, we’ll compare these two and understand when to use each.

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What is a Security Group?

A Security Group (SG) acts as a virtual firewall for your EC2 instances or resources. It allows you to define which traffic is allowed or denied at the instance level.

Key Features:

• Stateful: If an inbound rule allows traffic, the response is automatically allowed (no need to define outbound rules explicitly).

• Instance-level control: Each EC2 instance or resource can have one or more associated security groups.

• Inbound and outbound rules: You explicitly define both.

• Limited scope: Works only at the instance level (EC2, RDS, etc.).

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What is a Network Access Control List (NACL)?

A Network ACL is an optional firewall-like layer for controlling traffic at the subnet level within a VPC. It provides an extra layer of security for inbound and outbound traffic at the subnet boundary.

Key Features:

• Stateless: Both inbound and outbound rules must be explicitly defined (e.g., if inbound traffic is allowed, outbound traffic isn’t automatically allowed).

• Subnet-level control: All resources within the subnet are affected by the associated NACL.

• Numbered rules: Rules are evaluated in order, starting from the lowest-numbered rule.

• Default behavior: Comes with a default NACL that allows all traffic unless modified.

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Key Differences Between Security Groups and NACLs

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When to Use Security Groups vs NACLs

• Use Security Groups when you need instance-specific control (e.g., allowing SSH traffic only to a specific EC2 instance).

• Use NACLs to enforce network-wide rules (e.g., block a specific IP address across an entire subnet).

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Conclusion

Both Security Groups and NACLs are vital tools for managing network security within AWS. Security Groups are best for fine-grained, resource-level control, while NACLs offer broader subnet-level control. Understanding their differences and how to apply them effectively will help you better secure your AWS environments.

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Happy securing your cloud infrastructure! 🚀