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AWS Network Access Control Lists (NACLs): Overview and Configuration Example
AWS Network Access Control Lists (NACLs) act as a firewall for controlling traffic in and out of subnets in Amazon Virtual Private Cloud (Amazon VPC). NACLs operate at the subnet level and are stateless, allowing you to define rules to control both inbound and outbound traffic. Here's a detailed overview of AWS NACLs along with a configuration example:
Features of AWS NACLs:
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Subnet-Level Control:
- Control traffic at the subnet level within an Amazon VPC.
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Stateless Filtering:
- NACLs are stateless, meaning that rules for inbound and outbound traffic are separate.
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Rule Evaluation Order:
- Rules are evaluated based on rule number, with lower numbers taking precedence.
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Allow and Deny Rules:
- Define rules to allow or deny traffic based on IP addresses, protocols, and ports.
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Default Deny:
- Adheres to a default deny rule, meaning that all traffic is denied unless explicitly allowed.
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Numbered Rules:
- Rules are assigned numbers, and they are processed in numerical order.
Configuration Example:
Let's create a simple AWS Network ACL and define inbound and outbound rules for a subnet using the AWS Management Console:
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Login to AWS Console:
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Open VPC Console:
- Click on the "VPC" service in the console.
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Create Network ACL:
- In the VPC Dashboard, navigate to "Network ACLs" in the left navigation pane.
- Click "Create Network ACL" and provide a name for the NACL.
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Define Inbound Rules:
- Click on the newly created NACL and navigate to the "Inbound Rules" tab.
- Click "Add Rule" and define inbound rules based on your use case. For example, allow incoming traffic on port 80 for HTTP.
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Define Outbound Rules:
- Click on the "Outbound Rules" tab.
- Click "Add Rule" and define outbound rules. Typically, you might allow all outbound traffic.
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Associate NACL with Subnet:
- Associate the newly created NACL with the desired subnet. In the NACL details, click "Associations" and associate the NACL with a subnet.
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Test Connectivity:
- Deploy resources within the associated subnet and test connectivity. Ensure that inbound and outbound traffic follows the defined rules.
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Update NACL Rules (Optional):
- If your requirements change, update the NACL rules accordingly.
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Monitor NACL Activity:
- Monitor NACL activity using CloudWatch logs or other monitoring tools.
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Delete NACL (Optional):
- Optionally, you can delete the NACL through the console if it's no longer needed.