AWS WAF ASN Matching: Professional Guide to Network-Origin Traffic Control

Effectively managing where your web traffic originates is a cornerstone of modern web security. AWS WAF’s ASN (Autonomous System Number) matching feature equips you with precise control over access to your web applications, enabling you to allow or block requests based on their network origin. This guide explains the feature’s value, practical use cases, and provides a clear, professional walkthrough for implementation.

Understanding ASNs

An Autonomous System Number (ASN) uniquely identifies a network on the internet, functioning similarly to a digital zip code for routing traffic. For example, AS16509 is Amazon network, recognizing these identifiers allows you to make informed and strategic decisions about which networks can interact with your applications.

Why Use AWS WAF ASN Matching?

AWS WAF’s ASN matching acts as a powerful filter for your web traffic. By leveraging this feature, you can: • Allow or block traffic from specific networks or ISPs. • Respond rapidly to malicious activity by blocking entire networks. • Restrict access to trusted CDN providers. • Enforce zero-trust security models with granular network controls. This capability is particularly valuable when combined with other AWS WAF rules, enabling sophisticated, layered security policies.

Common Use Cases

• Regional Restrictions: Limit access to your application based on known ISPs within certain countries.

• Threat Mitigation: Block networks associated with suspicious or malicious activity.

• Content Delivery Optimization: Whitelist only approved CDN or partner networks.

• Zero-Trust Implementation: Specify exactly which networks are permitted to access sensitive resources.

Step-by-Step Implementation

Step 1: Identify Target ASNs

• Conduct thorough research to determine the ASNs you intend to allow or block. Utilize reputable tools such as Whois to obtain accurate ASN information. • Document all findings, including the rationale for targeting specific ASNs, to ensure traceability and facilitate future audits.

Step 2: Access the AWS WAF Console

• Log in to the AWS Management Console and navigate to the AWS WAF service.

• Initiate the creation of a new Web ACL or select an existing one for modification.

Step 3: Associate AWS Resources

• Select the appropriate resource type (e.g., CloudFront distribution, Application Load Balancer) to protect.

• Provide a clear description and assign a CloudWatch metric name for monitoring purposes.

• Click “Add AWS resource” to associate your selected resource with the Web ACL.

• Click “Next”

Step 4: Initiate Rule Creation

• Click the “Add” button to begin defining a new rule within your Web ACL.

• Choose “Add my own rules and rule group” to create a custom rule.

Step 5: Configure Rule Details

• Assign a descriptive name to the rule for easy identification.

• Select the rule builder scope (e.g., regional or global) based on your application’s deployment.

Step 6: Define Statement Criteria

• Specify the statement logic using AND, OR, or NOT operators to combine multiple conditions if needed, allowing for granular control.

• In the “Inspect” dropdown, select “Originates from an ASN in.”

• Enter the target ASNs as a comma-separated list. Ensure each ASN is within the valid range (0–4294967295).

• Select the desired action: Allow, Block, Count, or CAPTCHA. For initial deployment, “Count” is recommended to assess impact without enforcing the rule.

Step 7: (Optional) Use JSON Editor

• For advanced configurations, utilize the JSON editor to define the rule in JSON format. This approach provides greater flexibility and precision.

Step 8: Finalize and Add the Rule

• Click “Add” to include the rule in your Web ACL configuration.

Step 9: Set Rule Priority

• If multiple rules exist, assign a priority to determine the order in which traffic is evaluated. Higher-priority rules are processed first, ensuring critical controls are enforced promptly.

Step 10: Configure Metrics

• Define a metric name for monitoring rule performance via CloudWatch. This facilitates ongoing analysis and optimization.

Step 11: Review and Deploy

• Carefully review your Web ACL configuration, ensuring all rule logic and associations are correct.

• Click “Create web ACL” to deploy the configuration.