Set up and manage VPC Network Peering

Google Cloud VPC Network Peering enables internal IP address connectivity across two Virtual Private Cloud (VPC) networks, regardless of whether they belong to the same project or the same organization. Peering supports connectivity between networks having any combination of IPv4-only, dual-stack, and IPv6-only (Preview) subnets.

For more information, see VPC Network Peering.

Create a peering configuration

Before you begin, you must have the name of the VPC network to which you will peer with. If that network is located in another project, you must also have the project ID of that project. You can't list peering requests for your VPC network. If necessary, ask the administrator of the network that you intend to peer with for the network and project names.

A peering configuration establishes the intent to connect to another VPC network. Your network and the other network are not connected until each one has a peering configuration for the other. After the other network has a corresponding configuration to peer with your network, the peering state changes to ACTIVE in both networks, and they are connected. If there's no matching peering configuration in the other network, the peering state remains INACTIVE, indicating that your network is not connected to the other one.

Google Cloud allows only one peering-related activity at a time across peered networks. For example, if you set up peering with one network and immediately try to set up another, the operation fails with the following: Error: There is a peering operation in progress on the local or peer network. Try again later.

After connected, the two VPC networks always exchange IPv4 subnet routes (primary and secondary IPv4 subnet ranges) that use private IPv4 address ranges. For more information about subnet route exchange options, see Options for exchanging subnet routes. For details about exchanging static or dynamic routes, see Options for exchanging static routes and Options for exchanging dynamic routes.

gcloud compute networks peerings create PEERING_NAME \
    --network=NETWORK \
    --peer-project=PEER_PROJECT_ID \
    --peer-network=PEER_NETWORK_NAME \
    [--stack-type=STACK_TYPE] \
    [--import-custom-routes] \
    [--export-custom-routes] \
    [--import-subnet-routes-with-public-ip] \
    [--export-subnet-routes-with-public-ip]

module "peering1" {
  source        = "terraform-google-modules/network/google//modules/network-peering"
  version       = "~> 9.0"
  local_network = var.local_network # Replace with self link to VPC network "foobar" in quotes
  peer_network  = var.peer_network  # Replace with self link to VPC network "other" in quotes
}

Verify that traffic is passing between peered VPC networks

You can use VPC Flow Logs to view network flows sent from and received by VM instances. You can also use Firewall Rules Logging to verify that traffic is passing between the networks. Create VPC firewall rules that allow (or deny) traffic between the peered networks, and turn on Firewall Rules Logging for those rules. You can then view which firewall rules were hit using Cloud Logging.

Update a peering connection

When you update an existing VPC Network Peering connection, you can do the following:

• Change whether your VPC network exports or imports custom routes or privately used public IPv4 subnet routes to or from the peer VPC network.
• Update an existing peering connection to enable or disable the exchange of IPv6 routes between the peering networks.

Your network imports routes only if the peer network is also exporting the routes, and the peer network receives routes only if it imports them.

gcloud compute networks peerings update PEERING_NAME \
    --network=NETWORK \
    [--stack-type=STACK_TYPE] \
    [--import-custom-routes] \
    [--export-custom-routes] \
    [--export-subnet-routes-with-public-ip] \
    [--import-subnet-routes-with-public-ip]

List peering connections

List existing peering connections to view their status and whether they're importing or exporting custom routes.

gcloud compute networks peerings list

List peering routes

gcloud compute networks peerings list-routes PEERING_NAME \
    --network=NETWORK \
    --region=REGION \
    --direction=DIRECTION

Delete a VPC Network Peering connection

You or a network administrator for the peer VPC network can delete a peering configuration. When a peering configuration has been deleted, the peering connection switches to INACTIVE in the other network, and all routes shared among the networks are removed.

gcloud compute networks peerings delete PEERING_NAME \
    --network=NETWORK

Troubleshooting

The following sections describe how to troubleshoot issues with VPC Network Peering.

Peer VMs are unreachable

After the peering connection is ACTIVE, it may take up to a minute for all the traffic flows to be set up between the peered networks. This time depends on the size of the networks that are peering. If you have recently set up the peering connection, wait up to a minute and try again. Also, ensure that there are no firewall rules blocking access to/from peer VPC network subnet CIDRs.

Custom routes are missing

This section describes how to troubleshoot missing custom routes.

Check the peering connection state

To check the state of your peering connection, do the following:

1. List peering connections.
2. Identify the peering connection to troubleshoot, and review its peering state.
   1. If the state is ACTIVE, follow the steps in the next section.
   2. If the peering state is INACTIVE, a network administrator for the other network needs to create a peering configuration to your VPC network.

Troubleshoot an ACTIVE connection

To troubleshoot missing custom routes in an ACTIVE peering connection:

1. List peering routes in your VPC network. In the Effective routes tab, do the following:

   1. Consider that the regions in which dynamic routes are programmed depends on the dynamic routing mode of the VPC network that exports custom routes. For more details, see Effects of the dynamic routing mode. In global dynamic routing mode, only the highest ranked dynamic route is programmed in regions that don't match the region of the next hop.

   2. Click the Show suppressed routes toggle to the on position, then check for your route. To view the reason why a route has been suppressed, point to the icon in the Status column. Google Cloud provides route conflict resolution on a region-by-region basis in the VPC network that imports routes using VPC Network Peering.

   3. Look for a warning indicating that your VPC network has reached the limit for the dynamic routes per region per peering group quota. If your VPC network has reached the limit for this quota, one or more peering dynamic routes aren't programmed. Because it's not possible to show exactly which peering dynamic routes aren't programmed, request a quota limit increase for the dynamic routes per region per peering group quota.

2. If you still don't see the route you expect, do the following:

   1. Review your peering configuration, and update your peering configuration if necessary so that it imports custom routes.

   2. Ensure that the route is not one of the following route types that can't be exchanged using VPC Network Peering:

      • Peering subnet, peering static, and peering dynamic routes in a peered VPC network that are received from its other peer networks cannot be exchanged to your VPC network using VPC Network Peering.

      • Static routes that use the default internet gateway next hop and static routes with network tags cannot be exchanged using VPC Network Peering.

      For more information, see Route exchange options.

   3. Ask a network administrator of the peered VPC network to:

      1. List routes in their VPC network, looking for the route you expect.

      2. Review their peering configuration, and update the peering configuration if necessary so that it exports custom routes.

Traffic destined for a peer network is being dropped

You can use Connectivity Tests to help determine why traffic destined for a peer network is being dropped. If traffic should be sent using custom routes, see Custom routes are missing.

Traffic is being sent to an unexpected next hop

You can use Connectivity Tests to help determine why traffic is being sent to an unexpected next hop. If traffic should be sent using custom routes, see Custom routes are missing.

Unable to peer with a particular VPC network

If you cannot create a peering configuration with certain VPC networks, an organization policy might be constraining the VPC networks that your network can peer with. In the organization policy, add the network to the list of allowed peers or contact your organization administrator. For more information, refer to the constraints/compute.restrictVpcPeering constraint.

IPv6 routes are not exchanged

First, verify that both your peering connection and the peering connection of the peered VPC network have their stack types set to IPV4_IPV6. If necessary:

• Update your peering connection to set its stack type to IPV4_IPV6.
• Ask a network administrator of the peered VPC network to update their peering connection, setting its stack type to IPV4_IPV6.

After both peering connections have their stack types set to IPV4_IPV6, IPv6 subnet routes (both internal and external) are exchanged. IPv6 subnet routes are unique among all Google Cloud VPC networks.

To exchange IPv6 custom routes:

• Update your peering connection to import and export custom routes.
• Ask a network administrator of the peered VPC network to update their peering connection to import and export custom routes.

What's next

• For more information about VPC routing, see Routes.
• For limits related to VPC Network Peering, see VPC Network Peering limits.
• For information about how to use an internal passthrough Network Load Balancer as the next hop for a custom static route, see Use an internal passthrough Network Load Balancer as a next hop.