Struggling to connect Azure virtual networks securely and efficiently? Azure Virtual Network (VNet) Peering is the fundamental service you need to know. This essential networking feature enables seamless, private connectivity between two Azure VNets, allowing resources to communicate with low latency and high bandwidth as if they were on the same network. Unlike public internet routes, VNet Peering traffic travels exclusively through the Microsoft global backbone infrastructure, enhancing both security and performance. In this guide, we’ll explain how VNet Peering works, its key benefits over other connection methods, and provide a step-by-step tutorial to configure it for your cloud environment, ensuring your architecture is robust, scalable, and cost-effective.

1. Core Concept: What is Peering?

• Definition: Peering is the process of directly connecting two distinct networks to exchange traffic. In Azure, it specifically refers to connecting a Microsoft network (like a Virtual Network – VNet) to another network.
• Primary Goal: To enable private, low-latency, and high-bandwidth communication between the peered networks. Traffic stays on the Microsoft global backbone network and never traverses the public internet.
• Key Benefit: Enhanced security and performance compared to sending traffic over the public internet.

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2. The Three Types of Azure Peering

It’s crucial to understand the three distinct types, as they serve different purposes and have different characteristics.

 

 

 

• Important Clarification: Often, the term “Azure Peering” is used loosely. Remember:
  • VNet Peering is for connecting VNets to other VNets.
  • Microsoft Peering is a part of ExpressRoute for connecting on-premises to Microsoft’s public services.

3. Deep Dive: VNet Peering

This is the most common type of peering for intra-Azure connectivity.

• Types of VNet Peering:
  • Regional (Intra-region): Peering between VNets in the same Azure region (e.g., VNet-A in East US to VNet-B in East US). Very low latency.
  • Global (Inter-region): Peering between VNets in different Azure regions (e.g., VNet-A in East US to VNet-C in West Europe). Latency is higher than regional but much lower than going over the internet.
• Key Properties & Benefits:
  • Transitive Routing: NOT supported. If VNet-A is peered with VNet-B, and VNet-B is peered with VNet-C, VNet-A cannot talk to VNet-C through VNet-B. You need a network virtual appliance (NVA) or Azure VPN Gateway in the hub VNet.

• • Gateway Transit:Supported. A peered VNet can use the gateway (VPN/ExpressRoute) in another VNet (the hub). This is a fundamental concept for Hub-Spoke networks.
    • Allow Gateway Transit: Enable on the hub VNet peering.
    • Use Remote Gateways: Enable on the spoke VNet peering.
  • Network Traffic: Private, encrypted, and stays on the Azure backbone. No public internet involved.
  • Bandwidth: The bandwidth is based on the VM sizes or the VPN gateway SKU, not an artificial peering limit.
• Requirements and Constraints:
  • VNets must have non-overlapping IP address spaces.
  • Peering is a distinct resource with its own status (Initiated, Connected).
  • You can peer VNets across different Azure subscriptions and even different Azure Active Directory tenants.

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4. Deep Dive: Microsoft Peering (via ExpressRoute)

This is for connecting your on-premises network to Microsoft’s cloud services.

• What it Connects: Your corporate WAN (via an ExpressRoute circuit at a partner location) to Microsoft’s public endpoints.
• What You Can Access:
  • Microsoft 365 services (Exchange Online, SharePoint Online, Teams)
  • Azure Public Services (e.g., Azure Storage, SQL Database, Azure DevOps)
  • Power BI services
• Key Benefit: Traffic for these services travels over the private ExpressRoute connection, providing predictable performance, higher security, and reliability compared to the public internet.
• How it Works:
  1. You procure an ExpressRoute circuit from a connectivity provider.
  2. You enable Microsoft Peering on that circuit.
  3. You advertise your public IP prefixes (via BGP) to Microsoft over this peering.
  4. Microsoft advertises the IPs of its public services to you.
  5. Your on-premises network now routes traffic for these services directly over the private link.

 

 

 

6. Key Takeaways & Best Practices

1. Choose the Right Tool:
   • VNet-to-VNet? -> Use VNet Peering.
   • On-premises to Azure VNet? -> Use VPN (cheaper, internet) or ExpressRoute (expensive, private, high-perf).
   • On-premises to Microsoft Public Services (M365)? -> Use ExpressRoute with Microsoft Peering.
   • Large-scale global network? -> Consider Azure Virtual WAN.
2. Plan Your IP Address Space: Ensure all networks (VNets, on-premises) have non-overlapping CIDR blocks. This is the most common cause of peering failures.
3. Understand Transitivity: VNet Peering is non-transitive. For a hub-spoke model, enable Gateway Transit on the hub VNet.
4. Security: Use Network Security Groups (NSGs) to filter traffic between peered VNets. Peering establishes connectivity, but NSGs enforce security rules.
5. Cost Awareness: While peering itself has no hourly fee, data transfer between VNets in different regions (Global Peering) incurs outbound data transfer charges. Intra-region peering has no data transfer cost.

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7. Summary of Key Terms

• VNet (Virtual Network): A logically isolated network in Azure.
• VNet Peering: A connection between two VNets.
• ExpressRoute: A private connection from your premises to Microsoft cloud services.
• Microsoft Peering: A routing domain on an ExpressRoute circuit for accessing public Microsoft services.
• BGP (Border Gateway Protocol): The standard routing protocol used to exchange routing information across the internet and in private networks (used by ExpressRoute).