Introduction to Azure NAT Gateway

Azure NAT Gateway is a fully managed and highly resilient Network Address Translation (NAT) service. It provides simplified outbound connectivity for virtual networks, allowing virtual machines and other Azure resources to access the internet or other Azure services without requiring public IP addresses on the individual resources. This enhances security by abstracting the source IP addresses for outbound traffic.

NAT Gateway is designed for simplicity and scalability, offering predictable outbound IP addresses and improving the manageability of your network infrastructure.

Key Features

  • Simplified Outbound Connectivity: Eliminates the need to assign public IP addresses to individual VMs.
  • Predictable Outbound IPs: Uses a static set of public IP addresses, making it easier to manage firewall rules on external services.
  • High Resilience and Scalability: Built on Azure's robust infrastructure, offering high availability and automatic scaling.
  • Large SNAT Port Allocation: Provides a large pool of SNAT ports to prevent port exhaustion, supporting high-volume outbound connections.
  • Flow Timeout Control: Customizable TCP idle timeout for outbound connections.
  • Secure by Design: Reduces the attack surface by not exposing individual resources to the internet.
  • Regional Service: Deployed within an Azure region and associated with a specific virtual network.

How Azure NAT Gateway Works

When you associate an Azure NAT Gateway with a subnet in your virtual network, all outbound traffic originating from resources within that subnet is automatically routed through the NAT Gateway. The NAT Gateway translates the private IP addresses of your resources to one or more of its configured public IP addresses before sending the traffic to the internet or other Azure services.

When response traffic returns, the NAT Gateway uses its NAT table to translate the destination public IP address back to the correct private IP address of the originating resource.

SNAT Ports

Each public IP address associated with a NAT Gateway provides 64,512 SNAT ports. These ports are dynamically allocated to outbound connections. Azure NAT Gateway's large SNAT port capacity is crucial for applications that initiate many short-lived outbound connections.

For detailed information on SNAT port allocation and management, refer to the official Azure documentation on SNAT port exhaustion.

Deployment and Configuration

Deploying Azure NAT Gateway involves a few key steps:

  1. Create a NAT Gateway Resource: In the Azure portal, create a new NAT Gateway resource.
  2. Configure Public IP Addresses: Associate one or more public IP addresses (or public IP prefixes) with the NAT Gateway. These will be the source IPs for outbound traffic.
  3. Associate with a Subnet: Link the NAT Gateway to a subnet within your virtual network. All resources in this subnet will then use the NAT Gateway for outbound connections.

You can deploy NAT Gateway using the Azure portal, Azure CLI, PowerShell, or ARM templates.

Example using Azure CLI:


az network nat gateway create \
  --resource-group MyResourceGroup \
  --name MyNatGateway \
  --public-ip-addresses MyPublicIp \
  --idle-timeout 4 \
  --location eastus

After creating the NAT Gateway, associate it with a subnet: 


az network vnet subnet update \
  --resource-group MyResourceGroup \
  --vnet-name MyVnet \
  --name MySubnet \
  --nat-gateway MyNatGateway

Best Practices

  • Use Public IP Prefixes: For predictable and contiguous IP ranges, use public IP prefixes.
  • Monitor SNAT Port Usage: Keep an eye on SNAT port utilization to prevent exhaustion, especially for high-traffic applications.
  • Consider Inbound Traffic: NAT Gateway is for outbound connections only. For inbound traffic, you will need to use Load Balancers, Application Gateways, or individual public IP addresses.
  • Regional Deployment: Deploy NAT Gateway in the same region as your virtual network and resources for optimal performance.
  • Multiple Public IPs: Associate multiple public IP addresses or prefixes to increase the SNAT port capacity and provide IP redundancy.

Pricing

Azure NAT Gateway pricing is based on the following:

  • NAT Gateway Hours: A fixed hourly rate for each NAT Gateway deployed.
  • Data Processed: A charge for the amount of data processed through the NAT Gateway.
  • Public IP Address Hours: Standard charges for the public IP addresses or prefixes associated with the NAT Gateway.

For the most up-to-date pricing information, please visit the official Azure NAT Gateway pricing page.