Azure Private Resolver: Simplify DNS

When building networks in the cloud, DNS (Domain Name System) is essential for ensuring your resources can communicate smoothly. Azure Virtual WAN (vWAN) is often used to connect networks in different locations, and Azure Private Resolver makes managing DNS in this setup easier, faster, and more secure. In this blog, we’ll explore what Azure Private Resolver is, why it’s useful, and how to set it up in a multi-hub vWAN.

What is Azure Private Resolver?

Azure Private Resolver is a service that helps resolve DNS queries for private resources. It forwards DNS requests between Azure, on-premises networks, and private endpoints. This keeps queries off the public internet, ensuring secure and reliable communication.

Key Features of Azure Private Resolver

• Managed Service: No need to set up or maintain your own DNS servers.

• Always Available: Built for consistent uptime without interruptions.

• Secure Connections: DNS queries stay private and don’t go through the public internet.

• Supports Hybrid Environments: Works seamlessly with on-premises networks and Azure resources.

Scenario: Multi-Hub Azure Virtual WAN

In a multi-hub vWAN, you might have different regions connected through Azure hubs. These hubs can manage traffic for different parts of your network. You need DNS to work seamlessly between hubs and on-premises locations.

Azure Private Resolver helps by forwarding DNS queries to the right destination, whether it’s an Azure service, a private endpoint, or an on-premises server.

Steps to Set Up Azure Private Resolver in vWAN

1. What You Need

• Azure Virtual WAN with at least two hubs.

• A connection between Azure and your on-premises networks using ExpressRoute or VPN.

• Private DNS zones set up in Azure.

• Proper permissions for your Azure subscription.

2. Create Azure Private Resolver

1. Go to the Azure Portal.
   
   

2. Search for "Private DNS Resolver" and select it.
   
   

3. Click Create and set the following options:
   
   

   1. Resource Group: Select an existing group or create a new one.
      
      

   2. Region: Choose the same region as one of your hubs.
      
      

   3. Virtual Network: Select the vNet connected to your hub. This should be a dedicated vNet with two subnets—one for inbound traffic and one for outbound traffic, with no other resources on it.
      
      Note: If you have User-Defined Routes (UDRs) pointing traffic to a firewall or virtual appliance, ensure these routes don’t bypass inter-vNet traffic. Misconfigurations here can lead to issues with threat detection or DNSSec policies.
      
      

4. Add DNS rules to specify how queries should be forwarded.
   
   

   1. Include redundancy by setting up rules for failover.

5. Review your settings and deploy the resolver.
   
   

3. Set Up DNS Rules

1. Open the Private Resolver’s Ruleset section.

2. Add rules for specific DNS zones, such as:

   • Forward *.internal.mycompany.com to your on-premises DNS.

   • Forward *.azure.mycompany.com to Azure Private DNS zones.

3. Test the rules to ensure they resolve queries correctly.

4. Connect Private Resolver to vWAN

1. Link the vNet with the Private Resolver to your hub.

2. Configure routing in the vWAN to handle DNS traffic between hubs and on-premises locations.

3. If you’re using Azure Firewall, enable DNS Proxy to inspect and forward DNS traffic.

5. Test the Configuration

1. Use tools like nslookup or dig from a virtual machine in your network to verify DNS queries.

2. Ensure that internal queries are resolved by the Private Resolver and external queries use Azure DNS or another public resolver.

Planning DNSSec and Threat Detection Policies for Azure Private Resolver

When using Azure Private Resolver, it’s important to consider DNS Security Extensions (DNSSec) policies. DNSSec helps validate DNS queries and responses to ensure they are authentic and haven’t been tampered with. Misconfigured DNSSec policies can interfere with the resolver’s functionality, potentially blocking all externally bound DNS traffic.

Where DNSSec Applies in the Transaction Process

1. Client-Side Enforcement: DNSSec validation should occur at the client server level, before the query reaches the Private Resolver.

2. DNS Forwarding Rules: Forwarding rules in the resolver must align with DNSSec or threat detection policies to prevent mismatches.

3. Azure Firewall or Virtual Appliance: Use Azure Firewall to enforce DNSSec policies and inspect DNS traffic for compliance before it reaches the resolver.

Best Practices for DNSSec with Azure Private Resolver

• Validate Policies at the Source: Configure DNSSec on client systems to ensure DNS queries meet requirements before hitting the resolver.

• Prevent Overload: Avoid sending incorrectly validated queries to the resolver, as this can cause performance issues or block external DNS traffic.

• Monitor DNS Traffic: Use Azure Monitor or Log Analytics to track DNS traffic and identify DNSSec-related issues.

• Firewall Enforcement: Implement DNSSec rules in Azure Firewall to manage DNS traffic at the network edge.

Tips for Using Azure Private Resolver in vWAN

• Centralize DNS Management: Deploy one Private Resolver per region to simplify administration.

• Optimize Rules: Keep forwarding rules specific and efficient to improve performance.

• Plan for Failover: Deploy resolvers in paired regions to ensure redundancy and high availability.

Wrap-Up

Azure Private Resolver is a powerful tool for managing DNS in hybrid and multi-region networks. By integrating it into your multi-hub Azure Virtual WAN setup, you can achieve faster, more secure, and easier DNS resolution. This setup helps ensure your network remains reliable and scalable as your organization grows.

Ready to enhance your DNS strategy? Start deploying Azure Private Resolver in your vWAN today!

Have questions or want to share your experience? Drop a comment below or reach out for help with Azure networking.