Understanding VNet Peering
Virtual network (VNet) peering enables you to connect Azure virtual networks privately through the Azure backbone network. Once peered, VNets can communicate with each other as if they were one network. Traffic between peered VNets is private and remains within the Microsoft Azure network.
Benefits of VNet Peering
- Low Latency and High Bandwidth: Traffic between VNets uses the Microsoft backbone network, providing excellent performance.
- No Downtime for Applications: Peering is established without requiring applications to be re-architected.
- Secure Communication: Traffic between peered VNets remains on the Azure network, enhancing security.
- Simplified Network Management: Manage interconnected networks as a single logical entity.
- Global Reach: VNet peering can be established across different Azure regions.
Key Concepts
How VNet Peering Works
When you peer two VNets, you create a relationship that allows resources in each VNet to communicate directly. This is achieved through a private IP address connection. The following are key aspects:
- IP Address Spaces: Ensure that the IP address spaces of the peered VNets do not overlap. Overlapping address spaces will cause routing issues and prevent peering from working correctly.
- Routing: Azure automatically handles routing between peered VNets. You do not need to configure any gateways or complex route tables for basic connectivity.
- Bandwidth and Latency: Communication is routed over the Azure backbone network, offering high bandwidth and low latency.
- Resource Accessibility: Resources within the peered VNets can communicate using their private IP addresses.
Types of VNet Peering
VNet peering can be established in two ways:
- VNet-to-VNet Peering: Connects two VNets within the same Azure subscription.
- Global VNet Peering: Connects two VNets in different Azure regions. This is crucial for building resilient and distributed applications across geographical areas.
Peering Scenarios
VNet peering is commonly used in several scenarios:
- Development and Production Environments: Keep development, testing, and production environments separate while allowing them to communicate.
- Shared Services: A central VNet can host shared services (e.g., firewalls, DNS) and peer with other VNets that consume these services.
- Disaster Recovery: Establish peering between VNets in different regions for disaster recovery purposes, allowing failover to a secondary region.
- Multi-subscription Architectures: Connect VNets across different Azure subscriptions, often used by larger organizations.
Important Considerations:
- No Transitive Peering: VNet peering is not transitive. If VNet A is peered with VNet B, and VNet B is peered with VNet C, VNet A cannot communicate with VNet C through VNet B. You must explicitly peer VNet A with VNet C.
- Gateway Transit: By default, peered VNets cannot use the VPN or ExpressRoute gateways of the other VNet. You can enable gateway transit to allow one VNet to use the gateway of a peered VNet.
- Service Endpoints and Private Endpoints: VNet peering supports service endpoints and private endpoints, allowing secure access to Azure services.
Peering Properties
When configuring VNet peering, you'll encounter several properties:
| Property | Description |
|---|---|
| Remote VNet | The virtual network you are peering with. |
| Allow Virtual Network Access | Enables resources in the local VNet to access resources in the remote VNet. |
| Allow Gateway Transit | Allows traffic from the remote VNet to use the local VNet's gateway for access to on-premises networks or other VNets. |
| Use Remote Gateways | Allows the local VNet to use the remote VNet's gateway for access to on-premises networks or other VNets. |
| Peering state | Indicates the status of the peering connection (e.g., Initiated, Connected, Broken). |
Configuring VNet Peering
You can configure VNet peering through the Azure portal, Azure CLI, or Azure PowerShell. The process typically involves:
- Navigating to your virtual network in the Azure portal.
- Selecting the "Peerings" option.
- Clicking "Add" to create a new peering connection.
- Specifying the details of the remote VNet and the peering properties.
- Repeating the process on the remote VNet to establish a bidirectional connection.
For example, to create a peering connection using Azure CLI:
az network vnet peering create \
--resource-group MyResourceGroup \
--vnet-name MyVNet \
--name MyVNetToOtherVNet \
--remote-vnet MyOtherVNet \
--allow-vnet-access
Remember to configure peering in both directions: from your VNet to the remote VNet, and from the remote VNet back to your VNet.
Troubleshooting VNet Peering
Common issues include:
- Overlapping IP Address Spaces: The most frequent cause of connectivity problems.
- Incorrect Peering Configuration: Ensure "Allow Virtual Network Access" is enabled in both directions.
- Firewall Rules: Network Security Groups (NSGs) or Azure Firewall rules blocking traffic.
- Gateway Transit Issues: Incorrect configuration of gateway transit settings.
Utilize Azure Network Watcher's connection troubleshoot feature to diagnose connectivity issues.