Not every DNS query deserves an answer—especially not the ones leading to malicious domains or productivity-draining websites. Enter AWS Route 53 Resolver DNS Firewall, your trusty gatekeeper for managing and filtering DNS traffic at scale.

In this article, we’ll explore how AWS Route 53 DNS Firewall helps you say “no” to bad queries with finesse. Whether it’s blocking and restricting malicious domains or enforcing URL policies for compliance, you’ll learn why and how to deploy this powerful security tool.

Why Should You Filter DNS Queries?

Imagine your DNS as the phonebook of the internet, translating domain names to IP addresses. Without proper filters, this phonebook could become a directory for cyberattacks. Filtering DNS queries is crucial because:

1. It Prevents Cyber Threats: Blocks access to malicious domains used in phishing, malware delivery, and command-and-control attacks.
2. Enhances Policy Compliance: Enforces rules to ensure adherence to organizational or regulatory policies.

Boosts Productivity: Restricts non-essential websites, keeping users focused and reducing network strain.

Meet the AWS Route 53 Resolver DNS Firewall

AWS Route 53 Resolver DNS Firewall is a managed service that allows you to filter DNS queries in your Virtual Private Cloud (VPC). Here’s why it’s awesome:

• Custom Rules: Block or allow specific domains or domain patterns using rule groups.
• Threat Detection: Automatically update blocklists with intelligence from threat feeds.
• Ease of Deployment: Seamlessly integrate with existing AWS services, including CloudWatch for logging.

Scalability: Handle millions of queries without breaking a sweat.

Read more on AWS website : here 

How AWS DNS Filtering Works

Here’s how the DNS Firewall keeps the bad guys out:

1. DNS Query Inspection: It checks outgoing DNS queries against defined rule groups.
2. Rule Matching: If a query matches a blocked domain, it’s dropped or redirected, based on your rule settings.

Logging and Alerts: Logs are sent to CloudWatch or S3 for review and analysis.

Step-by-Step: Setting Up URL Filtering

Follow these steps to filter or block specific URLs:

High level summary steps:

Step 1: Enable DNS Firewall

1. Open the AWS Management Console and navigate to Route 53 Resolver.
2. Enable DNS Firewall for your VPC.

Step 2: Create a Rule Group

1. Define a rule group and specify actions for different URL patterns:
   • BLOCK malicious domains.
   • ALLOW trusted domains.
2. Use AWS-managed domain lists or upload custom lists.

Step 3: Associate Rule Group with a VPC

1. Link your rule group to one or more VPCs.
2. Ensure all DNS traffic from the VPC routes through the firewall.

Step 4: Test the Setup

1. Use a DNS query tool like dig to test allowed and blocked URLs.
2. Verify query outcomes in CloudWatch Logs.

Detailed Step Guide

1. Go to VPC 
2. Select Domain List
3. Add a domain list via domain list builder and review its created
4. 
5. 
6. Then select Rule groups from VPC 
7. 
8. Create a Rule Group 
9. Add a Rule (You can add your own domain list or AWS managed general domain list)
10. Apply Action as Block and select response as NXDOMAIN (indicates that the domain name that’s in the query doesn’t exist)
11. 
12. Verify the Rule was created
13. 
14. Then associate the VPC on which you wish to apply the Rule. The VPC may have internal resource examples like EC2 server etc… For this lab we will do EC2 server.
15. Wait for few seconds till VPC is enabled with status complete and verify
16. 
17. Then go to Route53 from search console
18. Select Query Logging 
19. 
20. Verify it was created. 
21. 
22. Then go to EC2 server (which represents an internal network on a VPC in this case)
23. Connect to an EC2 instance
24. Then try to reach the domain you have blocked. For this example we use facebook.com
    1. nslookup facebook.com
    2. 
25. If you wish to get more insights into the response when trying to resolve or reach a particular blocked domain name, type below command
    1. curl -vvv https://facebook.com -o /dev/null --max-time 5
    2. 
26. You can then also try to test a domain that is not blocked. You should get a response or domain should be resolved. 
    1. Nslookup google.com 
    2. 
27. You can check the query log in Amazon Cloudwatch as per the query log you created previously 
    1. Select Log groups on the left dashboard and choose the query log you created before.
    2. Then select Log streams
    3. Click search all log streams
    4. Type the name of the blocked domain. In this example its “facebook.com”
    5. Here you can see the blocked domain attempt to access was logged.
    6. 
28. Additionally you can keep adding more domains to the blocked domain list or also add AWS managed domain list 

Real-World Use Cases

• Preventing Malware Communication: Block domains used in command-and-control (C&C) attacks.
• Content Filtering for Businesses: Enforce acceptable use policies, e.g., restricting social media during work hours.

Securing IoT Devices: Stop DNS tunneling attacks that exfiltrate data through IoT endpoints.

Best Practices

• Regularly Update Blocklists: Use automated threat feeds to stay ahead of evolving threats.
• Monitor Logs Proactively: Review DNS logs in CloudWatch to detect anomalies.
• Combine with Other AWS Services: Use alongside AWS WAF and GuardDuty for comprehensive security.

Conclusion

AWS Route 53 Resolver DNS Firewall is your first line of defense against malicious DNS queries. By filtering and regulating outbound traffic, you can ensure a secure and productive network environment.

So, the next time a bad query knocks, let Route 53 Resolver DNS Firewall handle it. With this setup, not every question deserves an answer!