Create a Classic VPN connection to a remote site

You can configure a Classic VPN tunnel connection between an on-premises site and Google Cloud such that both the source and destination IP addresses are external (non-RFC 1918) IP addresses. For example, you can configure a Classic VPN connection to a remote site such that the on-premises IP address ranges do not conflict with the Google Cloud VM IP address.

In this tutorial, you use a Google Cloud project, the Google Cloud console, a virtual machine (VM) instance, Classic VPN, and a few Linux commands. To test the connection, you create a new VM instance to send and receive traffic between the VM and a remote peer.

Before you begin

1. Sign in to your Google Cloud account. If you're new to Google Cloud, create an account to evaluate how our products perform in real-world scenarios. New customers also get $300 in free credits to run, test, and deploy workloads.

2. In the Google Cloud console, on the project selector page, select or create a Google Cloud project.

   Note: If you don't plan to keep the resources that you create in this procedure, create a project instead of selecting an existing project. After you finish these steps, you can delete the project, removing all resources associated with the project.

   Go to project selector

3. Make sure that billing is enabled for your Google Cloud project.

4. In the Google Cloud console, on the project selector page, select or create a Google Cloud project.

   Note: If you don't plan to keep the resources that you create in this procedure, create a project instead of selecting an existing project. After you finish these steps, you can delete the project, removing all resources associated with the project.

   Go to project selector

5. Make sure that billing is enabled for your Google Cloud project.

6. Enable the Compute Engine API.

   Enable the API

7. On your workstation, install the gcloud command-line tool.
8. Configure the gcloud command-line tool to use your project. In the following command, replace PROJECT_ID with your project ID:

   gcloud config set project PROJECT_ID

9. Ensure that your on-premises subnets are connected to your on-premises VPN gateway.
10. Follow the instructions in Configuring the peer VPN gateway to configure the peer VPN gateway between Google Cloud and your on-premises VPN gateway.

Reserve a new static external IP address

In Compute Engine, each VM instance can have multiple network interfaces. Each interface can have both internal and external IP addresses. Forwarding rules can have external IP addresses for external load balancing or internal addresses for internal load balancing. To learn more about static IP addresses, see External IP addresses.

A static external IP address is the IP address that is reserved for your project until you decide to release it. If you have an IP address that your customers rely on to access your service, you can reserve that IP address so that only your project can use it. You can also promote an ephemeral external IP address to a static external IP address.

You can reserve two types of external IP addresses:

• A regional IP address that is used by VM instances with one or more network interfaces or by regional load balancers
• A global IP address that is used for global load balancers

For a list of regional and global load balancers, see the summary of Google Cloud load balancers.

Reserve a static external IP address by using the Google Cloud CLI or through the API. After you reserve the IP address, assign the IP address to a new instance while creating the new instance, or assign the IP address to an existing instance.

Console

1. Go to the Reserve a static address page.

   Go to Reserve a static address

2. Choose a name for the new address.

3. Specify whether it is an IPv4 or IPv6 address. IPv6 addresses can only be global and can only be used with global load balancers.

4. Specify whether this IP address is regional or global. If you are reserving a static IP address for an instance or for a regional load balancer, choose Regional. If you are reserving a static IP address for a global load balancer, choose Global.

5. If this is a regional IP address, select the region to create the address in.

6. Optional: Select a resource to attach to the IP address.

7. Click Reserve to reserve the IP address.

gcloud

To reserve a static external IP address using gcloud compute, use the compute addresses create command.

To reserve a global IP address, use the --global and --ip-version fields. For the --ip-version field, specify either IPV4 or IPV6. IPv6 addresses can only be global and can only be used with global load balancers.

Replace the ADDRESS_NAME with the name for this address.

gcloud compute addresses create ADDRESS_NAME \
    --global \
    --ip-version [IPV4 | IPV6]

To reserve a regional IP address, use the --region field:

gcloud compute addresses create ADDRESS_NAME  \
    --region=REGION

Replace the following:

• ADDRESS_NAME: the name for this address.
• REGION: the region in which to reserve this address. This region should be the same region as the resource to which the IP address is assigned. All regional IP addresses are IPv4.

Use the compute addresses describe command to view the result:

gcloud compute addresses describe ADDRESS_NAME

API

To create a regional IPv4 address, call the regional addresses.insert method:

POST https://compute.googleapis.com/compute/v1/projects/PROJECT_ID/regions/REGION/addresses

Your request body should contain the following:

{
  "name": "ADDRESS_NAME"
}

Replace the following:

• ADDRESS_NAME: the name of the address
• REGION: the name of the region for this request
• PROJECT_ID: the project ID for this request

For global static IPv4 addresses, call the globalAddresses.insert method:

POST https://compute.googleapis.com/compute/v1/projects/PROJECT_ID/global/addresses

Your request body should contain the following:

{
  "name": "ADDRESS_NAME"
}

For global static IPv6 addresses, call the globalAddresses.insert method:

POST https://compute.googleapis.com/compute/v1/projects/PROJECT_ID/global/addresses

Your request body should contain the following:

{
  "name": "ADDRESS_NAME",
  "ipVersion": "IPV6"
}

Use the addresses.get method to see the result.

Terraform

You can use a Terraform module to create an external IP address.

In the following example, the Terraform arguments have example values that you can change. The example creates three regional external IPv4 addresses.

module "address" {
  source       = "terraform-google-modules/address/google"
  version      = "~> 4.0"
  project_id   = var.project_id # Replace this with your service project ID in quotes
  region       = "europe-west1"
  address_type = "EXTERNAL"
  names = [
    "regional-external-ip-address-1",
    "regional-external-ip-address-2",
    "regional-external-ip-address-3"
  ]
}

The following example creates a global external IPv6 address:

resource "google_compute_global_address" "default" {
  project      = var.project_id # Replace this with your service project ID in quotes
  name         = "ipv6-address"
  address_type = "EXTERNAL"
  ip_version   = "IPV6"
}

Enable IP forwarding

You can enable IP forwarding when you create a VM, or by updating the canIpForward instance property on an existing VM. IP forwarding is enabled at the VM level and applies to all interfaces attached to the VM.

Important: Enabling IP forwarding is not sufficient to cause the instance to forward packets. You must configure its guest operating system as well.

Enable IP forwarding when you create a VM

These instructions describe how to enable IP forwarding when you create a VM. If you need to enable IP forwarding on an existing VM, update the canIpForward instance property.

Console

1. Go to the VM instances page.
   Go to VM instances
2. Click Create instance.
3. In Boot disk, ensure that you have selected a Linux image; for example, Debian GNU/Linux.
4. Click Networking, Disks, Security, Management, Sole-tenancy
5. Click Networking.
6. For IP forwarding, select Enable.
7. Specify any other instance parameters.
8. Click Create.

gcloud

When you create an instance using gcloud, add the --can-ip-forward flag to your command:

gcloud compute instances create ... --can-ip-forward

API

When you create an instance, use the canIpForward field to enable IP forwarding.

POST https://compute.googleapis.com/compute/v1/projects/PROJECT_ID/zones/ZONE/instances
{
  "canIpForward": true,
  ...other fields
}

Replace the following:

• PROJECT_ID: the ID of the project where your instance is created.
• ZONE: the Google Cloud zone where the instance is created.

For more information, refer to the instances.insert method.

Terraform

You can use the Terraform resource to create a VM instance with IP forwarding enabled.

In this example, the Terraform arguments have assigned values that you can change.

resource "google_compute_instance" "default" {
  project      = var.project_id # Replace this with your project ID in quotes
  zone         = "southamerica-east1-b"
  name         = "instance-next-hop"
  machine_type = "e2-medium"
  boot_disk {
    initialize_params {
      image = "debian-cloud/debian-9"
    }
  }
  network_interface {
    network = "default"
  }
  can_ip_forward = true
}

Create route for ingress traffic

Follow these steps to create a new static route. Before doing so, make sure that you are familiar with the following:

• static routes cannot have destination ranges that match or are more specific than the destination ranges used by any subnet route in your VPC network.

  • When using VPC Network Peering to connect two VPC networks, static routes in one network cannot have matching or more specific destinations than subnet routes in both of the networks. Google Cloud rejects static routes that would conflict with subnet routes in this way.

• To avoid conflicts when using an auto mode VPC network, don't create static routes whose destinations fit within 10.128.0.0/9. Review the auto mode IPv4 ranges for details.

• Destinations for static routes can't overlap with any internal allocated range.

• Make sure that you're familiar with instances as next hops before you create a custom-static route that uses a VM as its next hop. Google Cloud only validates that a VM exists at the time when you create the route if you choose a next hop instance.

• If you create a route using a network tag, then only VMs with that tag receive that route. However, tagged VMs still receive all routes that have no network tag.

Console

1. Go to the Routes page in the Google Cloud console.
   Go to Routes
2. Click Create route.
3. Specify a Name and a Description for the route.
4. Select an existing Network where the route will apply.
5. Specify a Destination IP range to define the destination of the route.
6. Specify a Priority for the route. A priority is only used to to determine routing order if routes have equivalent destinations. See Route parameters for more details.
7. To make the route applicable only to instances with matching network tags, specify those in the Instance tags field. Leave the field blank to make the route applicable to all instances in the network, or if you select an internal TCP/UDP load balancer as the route's next hop. Network tags don't apply to routes that have an internal TCP/UDP load balancer as a next hop.

8. Select a Next hop for the route:

   • Specify an instance allows you to select an instance by name. Traffic will be routed to that instance (or any replacement instance with the same name in the same zone) even if its IP address changes.
   • Specify IP address allows you to enter an IP address of an existing instance in the VPC network. Refer to Next hops and features for important restrictions on valid next hop IP addresses.

9. Click Create.

gcloud

Create a new static route:

gcloud compute routes create ROUTE_NAME \
    --destination-range=DESTINATION_RANGE \
    --network=NETWORK \
    NEXT_HOP_SPECIFICATION

Replace the placeholders:

• ROUTE_NAME is the name of the route.
• DESTINATION_RANGE represents the destination IP addresses to which this route will apply. The broadest possible destination is 0.0.0.0/0.
• NETWORK is the name of the VPC network that will contain the route.
• NEXT_HOP_SPECIFICATION represents the next hop for the static route. You must specify only one of the following as a next hop. For more information about the different types of next hops, see Next hops and features.
  • --next-hop-instance=INSTANCE_NAME and --next-hop-instance-zone=ZONE: Use this next hop to direct traffic to an existing VM instance by name and zone. Traffic is sent to the primary internal IP address for the VM's network interface located in the same network as the route.
  • --next-hop-address=ADDRESS: Use this next hop to direct traffic to the IP address of an existing VM instance.

To make the static route only apply to select VMs by network tag, add the --tags flag and specify one or more network tags. For more information about how network tags and static routes work together, see Applicable routes. You can use tags with any static route.

See the SDK documentation for additional information about the gcloud syntax.

API

Create a new static route.

POST https://compute.googleapis.com/compute/v1/projects/PROJECT_ID/global/routes
{
  "destRange": "DESTINATION_RANGE",
  "name": "ROUTE_NAME",
  "network": "NETWORK_NAME",
  "priority": PRIORITY,
  "NEXT_HOP_SPECIFICATION": VALUE
}

Replace the placeholders:

• PROJECT_ID is the ID of the project where your route is created.
• DESTINATION_RANGE represents the destination IP addresses to which this route will apply. The broadest possible destination is 0.0.0.0/0.
• ROUTE_NAME a name for the route.
• NETWORK_NAME is the name of the VPC network that will contain the route.
• The VALUE for the NEXT_HOP_SPECIFICATION represents the next hop for the static route. For NEXT_HOP_SPECIFICATION, you must specify only one of the following next-hop fields: nextHopIp,nextHopInstance. For more information about the different types of next hops and features, see Next hops and features.

For more information, refer to the routes.insert method.

Terraform

You can create a static route by using a Terraform module.

This static route creates a default route to the internet.

module "google_compute_route" {
  source       = "terraform-google-modules/network/google//modules/routes"
  version      = "~> 9.0"
  project_id   = var.project_id # Replace this with your project ID in quotes
  network_name = "default"

  routes = [
    {
      name              = "egress-internet"
      description       = "route through IGW to access internet"
      destination_range = "0.0.0.0/0"
      tags              = "egress-inet"
      next_hop_internet = "true"
    }
  ]
}

Create a Classic VPN using static routing

The VPN setup wizard is the only Google Cloud console option for creating a Classic VPN gateway. The wizard includes all required configuration steps for creating a Classic VPN gateway, tunnels, BGP sessions, and an external VPN gateway resource. However, you can complete certain steps later, such as configuring BGP sessions.

Note: The Create VPN gateway button only supports creating HA VPN gateways.

Console

Configure the gateway

1. In the Google Cloud console, go to the VPN page.

   Go to VPN

2. If you are creating a gateway for the first time, click Create VPN connection.

3. Select the VPN setup wizard.

4. Select the Classic VPN option button.

5. Click Continue.

6. On the Create a VPN connection page, specify the following gateway settings:

   • Name: The name of the VPN gateway. The name cannot be changed later.
   • Description: Optionally, add a description.
   • Network: Specify an existing VPC network in which to create the VPN gateway and tunnel.
   • Region: Cloud VPN gateways and tunnels are regional objects. Choose a Google Cloud region where the gateway will be located. Instances and other resources in different regions can use the tunnel for egress traffic subject to the order of routes. For best performance, locate the gateway and tunnel in the same region as relevant Google Cloud resources.
   • IP address: Create or choose an existing regional external IP address.

Configure tunnels

1. For the new tunnel, in the Tunnels section, specify the following settings:

   • Name: The name of the VPN tunnel. The name cannot be changed later.
   • Description: Optionally, type a description.
   • Remote peer IP address: Specify the external IP address of the peer VPN gateway.
   • IKE version: Choose the appropriate IKE version supported by the peer VPN gateway. IKEv2 is preferred if it's supported by the peer device.
     Known issue: When configuring VPN tunnels to AWS, use the IKEv2 encryption protocol and select fewer transform sets on the AWS side; otherwise, the Cloud VPN tunnel can fail to rekey. For example, select a combination of single Phase 1 and Phase 2 encryption algorithms, integrity algorithms, and DH group numbers.
     
     This rekeying issue is caused by a large Security Association (SA) payload size for the default set of AWS transform sets. This large payload size results in IP fragmentation of IKE packets on the AWS side, which Cloud VPN does not support.
   • IKE pre-shared key: Provide a pre-shared key (shared secret) used for authentication. The pre-shared key for the Cloud VPN tunnel must match the one used when you configure the counterpart tunnel on the peer VPN gateway. To generate a cryptographically strong pre-shared key, follow these directions.
   • Select policy-based tunnels
   • Under Routing options, select Policy-based.
   • Under Remote network IP ranges, provide a space-separated list of the IP address ranges used by the local traffic on the on-premises VPN setup.
   • In the Local IP ranges field, enter the external IP address range that you created earlier with a subnet prefix /32.
   • Click Done.
   • Click Create.

gcloud

To create a Cloud VPN gateway, complete the following command sequence. In the commands, replace the following:

• PROJECT_ID: the ID of your project
• NETWORK: the name of your Google Cloud network
• REGION: the Google Cloud region where you create the gateway and tunnel
• GW_NAME: the name of the gateway
• GW_IP_NAME: a name for the external IP address used by the gateway
• Optional: The --target-vpn-gateway-region is the region of the Classic VPN gateway to operate on. Its value should be the same as --region. If not specified, this option is automatically set. This option overrides the default compute/region property value for this command invocation.

Configure the gateway resources

1. Create the target VPN gateway object:

   gcloud compute target-vpn-gateways create GW_NAME \
      --network=NETWORK \
      --region=REGION \
      --project=PROJECT_ID
   

2. Reserve a regional external (static) IP address:

   gcloud compute addresses create GW_IP_NAME \
      --region=REGION \
      --project=PROJECT_ID
   

3. Note the IP address (so you can use it when you configure your peer VPN gateway):

   gcloud compute addresses describe GW_IP_NAME \
      --region=REGION \
      --project=PROJECT_ID \
      --format='flattened(address)'
   

4. Create three forwarding rules; these rules instruct Google Cloud to send ESP (IPsec), UDP 500, and UDP 4500 traffic to the gateway:

   gcloud compute forwarding-rules create fr-GW_NAME-esp \
      --load-balancing-scheme=EXTERNAL \
      --network-tier=PREMIUM \
      --ip-protocol=ESP \
      --address=GW_IP_NAME \
      --target-vpn-gateway=GW_NAME \
      --region=REGION \
      --project=PROJECT_ID
   

   gcloud compute forwarding-rules create fr-GW_NAME-udp500 \
      --load-balancing-scheme=EXTERNAL \
      --network-tier=PREMIUM \
      --ip-protocol=UDP \
      --ports=500 \
      --address=GW_IP_NAME \
      --target-vpn-gateway=GW_NAME \
      --region=REGION \
      --project=PROJECT_ID
   

   gcloud compute forwarding-rules create fr-GW_NAME-udp4500 \
      --load-balancing-scheme=EXTERNAL \
      --network-tier=PREMIUM \
      --ip-protocol=UDP \
      --ports=4500 \
      --address=GW_IP_NAME \
      --target-vpn-gateway=GW_NAME \
      --region=REGION \
      --project=PROJECT_ID
   

Create the Cloud VPN tunnel

1. In the commands, replace the following:

   • TUNNEL_NAME: a name for the tunnel
   • ON_PREM_IP: the external IP address of the peer VPN gateway
   • IKE_VERS: 1 for IKEv1 or 2 for IKEv2
     Known issue: When configuring VPN tunnels to AWS, use the IKEv2 encryption protocol and select fewer transform sets on the AWS side; otherwise, the Cloud VPN tunnel can fail to rekey. For example, select a combination of single Phase 1 and Phase 2 encryption algorithms, integrity algorithms, and DH group numbers.
     
     This rekeying issue is caused by a large SA payload size for the default set of AWS transform sets. This large payload size results in IP fragmentation of IKE packets on the AWS side, which Cloud VPN does not support.
   • SHARED_SECRET: your pre-shared key (shared secret). The pre-shared key for the Cloud VPN tunnel must match the one used when you configure the counterpart tunnel on the peer VPN gateway. To generate a cryptographically strong pre-shared key, follow these directions.

   For policy-based VPN:

   • LOCAL_IP_RANGES: a comma-delimited list of the Google Cloud IP address ranges. For example, you can supply the CIDR block for each subnet in a VPC network. This is the left side from the perspective of Cloud VPN.
   • REMOTE_IP_RANGES: a comma-delimited list of the peer network IP address ranges. This is the right side from the perspective of Cloud VPN.

   To configure a policy-based VPN tunnel, run the following command:

   gcloud compute vpn-tunnels create TUNNEL_NAME \
       --peer-address=ON_PREM_IP \
       --ike-version=IKE_VERS \
       --shared-secret=SHARED_SECRET \
       --local-traffic-selector=LOCAL_IP_RANGES \
       --remote-traffic-selector=REMOTE_IP_RANGES \
       --target-vpn-gateway=GW_NAME \
       --region=REGION \
       --project=PROJECT_ID
   

   For route-based VPN, both the local and remote traffic selectors are 0.0.0.0/0 as defined in routing options and traffic selectors.

   To configure a route-based VPN tunnel, run the following command:

   gcloud compute vpn-tunnels create TUNNEL_NAME \
       --peer-address=ON_PREM_IP \
       --ike-version=IKE_VERS \
       --shared-secret=SHARED_SECRET \
       --local-traffic-selector=0.0.0.0/0 \
       --remote-traffic-selector=0.0.0.0/0 \
       --target-vpn-gateway=GW_NAME \
       --region=REGION \
       --project=PROJECT_ID
   

2. Create a static route for each remote IP address range that you specified in the --remote-traffic-selector option in the previous step. Repeat this command for each remote IP address range. Replace ROUTE_NAME with a unique name for the route, and replace REMOTE_IP_RANGE with the appropriate remote IP address range.

   gcloud compute routes create ROUTE_NAME \
       --destination-range=REMOTE_IP_RANGE \
       --next-hop-vpn-tunnel=TUNNEL_NAME \
       --network=NETWORK \
       --next-hop-vpn-tunnel-region=REGION \
       --project=PROJECT_ID
   

   Note: The gcloud command to create a route uses the default priority of 1000. If you need to create a higher priority route, use the --priority flag with a lower number when you create the route. You cannot change the priority of a route after the route has been created; however, you can delete and replace the static route without needing to re-create the VPN tunnel. For details about how routes work in your VPC network, see Routes overview and Order of routes.

Configure the VM to send and receive traffic

To complete your setup and test whether you can send and receive traffic from the VM, follow these steps:

Receive traffic

1. In the Google Cloud console, go to the VM instances page.
2. In the list of virtual machine instances, find the VM that you created earlier and click SSH.

3. Create an IP address alias for the VM using the public IP address that you reserved earlier. You will be able to receive traffic to the VM after you complete this step.

   Run the following command:

   sudo ip address add EXTERNAL_IP_ADDRESS/32 dev eth0
   

   Replace EXTERNAL_IP_ADDRESS with the public IP address that you reserved earlier.

Send traffic

1. In the Google Cloud console, go to the VM instances page.
2. In the list of virtual machine instances, find the VM that you created earlier and click SSH.

3. Run the following command to test if you can ping an external IP address:

   $ ping -I EXTERNAL_IP_ADDRESS REMOTE_PEER_IP_ADDRESS
   PING 10.0.0.1 (10.0.0.1) from EXTERNAL_IP_ADDRESS : 56(84) bytes of data.
   64 bytes from 10.0.0.1: icmp_seq=1 ttl=64 time=4.46 ms
   64 bytes from 10.0.0.1: icmp_seq=2 ttl=64 time=1.11 ms
   

   Replace REMOTE_PEER_IP_ADDRESS with an IP address from the remote peer's subnet.

4. To enable the VM to automatically use this interface when sending traffic to the VPN tunnel, you can create an iptables rule.

   For example, run the following command to create an iptables rule:

   $ sudo iptables -t nat -A POSTROUTING --destination REMOTE_PEER_SUBNET -j SNAT --to-source EXTERNAL_IP_ADDRESS
   

   Replace REMOTE_PEER_SUBNET with the remote peer's subnet.

5. Run the following commands to test the Cloud VPN tunnel:

   $ ping REMOTE_PEER_IP_ADDRESS
   PING 10.0.0.1 (10.0.0.1) 56(84) bytes of data.
   64 bytes from 10.0.0.1: icmp_seq=1 ttl=64 time=3.48 ms
   64 bytes from 10.0.0.1: icmp_seq=2 ttl=64 time=1.42 ms
   

   $ ping EXTERNAL_IP_ADDRESS
   PING 35.195.72.19 (35.195.72.19) 56(84) bytes of data.
   64 bytes from 35.195.72.19: icmp_seq=1 ttl=64 time=0.033 ms
   64 bytes from 35.195.72.19: icmp_seq=2 ttl=64 time=0.062 ms