Is there a way to do a migration maintaining the same Ip Address?

Migrating an on-premises virtual network (VNET) to Azure while retaining the same IP addresses can be challenging but is possible through several approaches. The solution you referenced, subnet extension, can be part of the strategy, but it's not the only approach and may not be the most current or comprehensive method available.

Options for Migrating with Same IP Addresses

1. Azure VNET Peering with Overlapping Addresses

Azure Virtual Network (VNET) peering allows you to connect two VNETs in Azure. However, traditionally, VNET peering does not support overlapping IP address spaces. You would need to re-address your on-premises network or the Azure network to avoid conflicts.

2. Azure Virtual WAN

Azure Virtual WAN provides a way to connect multiple networks, including on-premises and Azure VNETs, but it also requires non-overlapping IP address spaces.

3. Azure VPN Gateway with Policy-Based VPN

Using a policy-based VPN can allow you to connect networks with overlapping IP addresses by defining specific traffic policies. However, this is generally more complex and may not be suitable for all scenarios.

4. Subnet Extension (Preview Feature)

The subnet extension feature, which is in preview, allows you to extend your on-premises subnets into Azure. This feature is designed for scenarios where you need to migrate workloads to Azure without changing IP addresses. However, being a preview feature, it may not be fully documented, and support may be limited.

Steps for Subnet Extension (Preview Feature)

1. Set Up Azure VNET
   • Create a VNET in Azure that does not overlap with your on-premises network initially.
2. Configure VPN Gateway
   • Set up a VPN gateway in Azure to establish a secure connection between your on-premises network and the Azure VNET.
3. Configure Subnet Extension
   • Follow the guidelines for configuring subnet extension. You may need to work closely with Microsoft support to ensure this is set up correctly, as the documentation is sparse and the feature is in preview.
4. Migrate Workloads
   • Start migrating your workloads to Azure using the extended subnet. Ensure that your routing and DNS configurations are correctly set up to handle the traffic between on-premises and Azure seamlessly.

Example Configuration for Subnet Extension

This example assumes you have already set up the VPN gateway and connected it to your on-premises network.

{

  "virtualNetwork": {

    "name": "ExtendedVNET",

    "location": "eastus",

    "properties": {

      "addressSpace": {

        "addressPrefixes": ["10.0.0.0/16"]

      },

      "subnets": [

        {

          "name": "ExtendedSubnet",

          "properties": {

            "addressPrefix": "10.0.0.0/24",

            "delegations": [],

            "privateEndpointNetworkPolicies": "Disabled",

            "privateLinkServiceNetworkPolicies": "Disabled"

          }

        }

      ]

    }

  }

}

Considerations

• Complexity and Support: Subnet extension is a complex and potentially unsupported feature. Ensure you have adequate support from Microsoft if you choose this route.
• Network Configuration: Proper routing and DNS configuration are critical to ensure smooth operation and connectivity between on-premises and Azure.
• Testing: Thoroughly test the configuration in a non-production environment before migrating critical workloads.

While it is possible to migrate an on-premises VNET to Azure while retaining the same IP addresses, it requires careful planning and configuration. The subnet extension feature is a potential solution, but due to its complexity and preview status, it may not be fully reliable. Working closely with Microsoft support and thoroughly testing the configuration is essential to ensure a successful migration.

If the subnet extension approach seems too risky or complex, consider re-addressing your network to avoid overlapping IP addresses, as this is a more straightforward and fully supported method.