Applies to

• Azure Virtual Network
• Local Network Gateway
• Site-to-Site VPN

 

Summary

This article explains how to add a subnet to the on-premises network configuration in Azure by updating the Local Network Gateway. This is required when you expand your on-premises network and need Azure to recognize the new subnet for VPN connectivity.

Prerequisites

• An existing Local Network Gateway configured in Azure.
• Administrative access to the Azure portal or Azure PowerShell.
• The new subnet CIDR block (e.g., 10.20.0.0/24) that you want to add.

Steps

1. Sign in to the Azure portal 

   1. Go to https://portal.azure.com.

2. Navigate to Local Network Gateway

   1. ​​​​​​​In the left-hand menu, select All services.

   2. Search for Local Network Gateways and select the gateway you want to update

3. Edit Address Space

   1. Under Settings, select Configuration.

   2. In the Address space section, click + Add.

   3. Enter the new subnet in CIDR format (e.g., 10.20.0.0/24)

4. Save Changes

   1. Click Save to apply the updated configuration.

Verification

• After saving, verify that the new subnet appears in the Address space list.
• Ensure your on-premises VPN device is configured to route traffic for the new subnet.