Cloud NAT overview

Cloud NAT provides network address translation (NAT) for outbound traffic to the internet, Virtual Private Cloud (VPC) networks, on-premises networks, and other cloud provider networks.

Cloud NAT provides NAT for the following Google Cloud resources:

Cloud NAT supports address translation for established inbound response packets only. It doesn't allow unsolicited inbound connections.

Types of Cloud NAT

In Google Cloud, you use Cloud NAT to create NAT gateways that let instances in a private subnet connect to resources outside your VPC network.

Using a NAT gateway, you can enable the following types of NAT:

  • Public NAT
  • Private NAT

You can have both Public NAT and Private NAT gateways offering NAT services to the same subnet in a VPC network.

Public NAT

Public NAT lets Google Cloud resources that do not have public IP addresses communicate with the internet. These VMs use a set of shared public IP addresses to connect to the internet. Public NAT does not rely on proxy VMs. Instead, a Public NAT gateway allocates a set of external IP addresses and source ports to each VM that uses the gateway to create outbound connections to the internet.

Consider a scenario in which you have VM-1 in subnet-1 whose network interface does not have an external IP address. However, VM-1 needs to connect to the internet to download critical updates. To enable connectivity to the internet, you can create a Public NAT gateway that is configured to apply to the IP address range of subnet-1. Now, VM-1 can send traffic to the internet by using the internal IP address of subnet-1.

For more information, see Public NAT.

Private NAT

Private NAT enables private-to-private NAT for the following traffic.

Traffic Description
From a VPC network to another VPC network Private NAT supports private-to-private NAT for VPC networks attached as VPC spokes to a Network Connectivity Center hub. For more information, see Private NAT for Network Connectivity Center spokes.
From a VPC network to a network outside of Google Cloud Private NAT supports the following options for traffic between VPC networks and on-premises or other cloud provider networks:

Assume that the resources in your VPC network need to communicate with the resources in a VPC network or an on-premises or other cloud provider network that is owned by a different business unit. However, that network contains subnets whose IP addresses overlap with the IP addresses of your VPC network. In this scenario, you create a Private NAT gateway that translates traffic between the subnets in your VPC network to the non-overlapping subnets of the other network.

For more information about Private NAT, see Private NAT.

Supported resources

The following table lists the Google Cloud resources supported by each type of Cloud NAT. The checkmark indicates that the resource is supported, and the symbol indicates that the resource isn't supported.

Resource Public NAT Private NAT
Compute Engine VM instances
GKE clusters
Cloud Run, Cloud Run functions, and App Engine standard environment
Regional internet NEGs Not applicable

Architecture

Cloud NAT is a distributed, software-defined managed service. It's not based on proxy VMs or appliances. Cloud NAT configures the Andromeda software that powers your Virtual Private Cloud (VPC) network so that it provides source network address translation (source NAT or SNAT) for resources. Cloud NAT also provides destination network address translation (destination NAT or DNAT) for established inbound response packets.

Traditional NAT versus Cloud NAT.
Traditional NAT versus Cloud NAT (click to enlarge).

Benefits

Cloud NAT provides the following benefits:

  • Security

    When using a Public NAT gateway, you can reduce the need for individual VMs to each have external IP addresses. Subject to egress firewall rules, VMs without external IP addresses can access destinations on the internet. For example, you might have VMs that only need internet access to download updates or to complete provisioning.

    If you use manual NAT IP address assignment to configure a Public NAT gateway, you can confidently share a set of common external source IP addresses with a destination party. For example, a destination service might only allow connections from known external IP addresses.

    A Private NAT gateway does not permit any resource from Network Connectivity Center connected VPC spokes to directly initiate a connection with the VMs inside overlapping subnetworks. When a VM in a Private NAT configuration tries to initiate a connection with a VM in another network, the Private NAT gateway performs SNAT by using the IP addresses from the Private NAT range. The gateway also performs DNAT on the responses to the outbound packets.

  • Availability

    Cloud NAT is a distributed, software-defined managed service. It doesn't depend on any VMs in your project or a single physical gateway device. You configure a NAT gateway on a Cloud Router, which provides the control plane for NAT, holding configuration parameters that you specify. Google Cloud runs and maintains processes on the physical machines that run your Google Cloud VMs.

  • Scalability

    Cloud NAT can be configured to automatically scale the number of NAT IP addresses that it uses, and it supports VMs that belong to managed instance groups, including the groups with autoscaling enabled.

  • Performance

    Cloud NAT does not reduce the network bandwidth per VM. Cloud NAT is implemented by Google's Andromeda software-defined networking. For more information, see Network bandwidth in the Compute Engine documentation.

  • Logging

    For Cloud NAT traffic, you can trace the connections and bandwidth for compliance, debugging, analytics, and accounting purposes.

  • Monitoring

    Cloud NAT exposes key metrics to Cloud Monitoring that give you insight into your fleet's use of NAT gateways. Metrics are sent automatically to Cloud Monitoring. There, you can create custom dashboards, set up alerts, and query metrics.

Product interactions

For more information about the important interactions between Cloud NAT and other Google Cloud products, see Cloud NAT product interactions.

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