Using VPC Network Peering

Google Cloud Platform (GCP) Virtual Private Cloud (VPC) Network Peering allows private RFC 1918 connectivity across two VPC networks regardless of whether or not they belong to the same project or the same organization.

For details on VPC Network Peering, see the VPC Network Peering Overview.

Creating 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.

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.

Once connected, the two networks always exchange subnet routes. You can optionally import both static and dynamic custom routes from a peered network if it has been configured to export them. For more information, see importing and exporting custom routes.

Console

  1. Go to the VPC Network Peering page in the Google Cloud Platform Console.
    Go to the VPC Network Peering page
  2. Click Create connection.
  3. Click Continue.
  4. Enter a Name for your peering connection.
  5. Under Your VPC network, select a network you want to peer.

  6. Select the network to peer with.

    • If the network that you want to peer with is in the same project, select In project [NAME-OF-YOUR-PROJECT] and then the network to peer with.
    • If the network that you want to peer with is in a different project, select In another project. Specify the project ID that includes the network you want to peer with and the name of the VPC network.

  7. To import or export custom routes, expand the Exchange custom routes section and then choose Import custom routes, Export custom routes, or both.

  8. Click Create.

gcloud

Create a VPC Network Peering connection. Use the --import-custom-routes and --export-custom-routes flags to import or export custom routes from or to the peered network.

gcloud beta compute networks peerings create [PEERING-NAME] \
    --network=[MY-LOCAL-NETWORK] \
    --peer-project [PEER-PROJECT-ID] \
    --peer-network [PEER-NETWORK-NAME] \
    [--import-custom-routes] \
    [--export-custom-routes]

Updating a peering connection

Update an existing VPC Network Peering connection to change whether your VPC network exports or imports custom routes to or from the peer VPC network.

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

Console

  1. Go to the VPC Network Peering page in the Google Cloud Platform Console.
    Go to the VPC Network Peering page
  2. Select the peering connection to update.
  3. Click Edit.
  4. Update your custom route settings by selecting or deselecting Import custom routes or Export custom routes.

gcloud

Update the peering connection to change your import or export settings for custom routes.

gcloud beta compute networks peerings update [PEERING-NAME] \
    --network=[MY-LOCAL-NETWORK] \
    [--[no-]import-custom-routes] \
    [--[no-]export-custom-routes]

Listing peering connections

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

Console

  1. Go to the VPC Network Peering page in the Google Cloud Platform Console to list all of the peering connections in your project.
    Go to the VPC Network Peering page
  2. Select the peering connection to view its details.

gcloud 

gcloud beta compute networks peerings list \
    --network=[MY-LOCAL-NETWORK]

Listing routes from peering connections

List the routes that your VPC network is importing from or exporting to a peered VPC network. For exported routes, you can check whether a peer network is accepting or rejecting your custom routes. For imported routes, you can check whether your network is accepting or rejecting custom routes from a peer network.

Console

  1. Go to the VPC Network Peering page in the Google Cloud Platform Console to list all of the peering connections in your project.
    Go to the VPC Network Peering page
  2. Select the peering connection to view its details.

  3. View customs routes that your network is importing or exporting. Use the region selector to view dynamic routes in a particular region. Subnet and static routes are global and are shown for all regions.

    • To view the imported custom routes, select the Imported routes tab.
    • To view the exported custom routes, select the Exported routes tab.

gcloud 

gcloud beta compute networks peerings list-routes [PEERING-NAME] \
    --network=[MY-LOCAL-NETWORK]
    --region=[REGION] \
    --direction=INCOMING|OUTGOING
  • The --region flag lists all dynamic routes from a particular region. Subnet and static routes are global and are shown for all regions.
  • The --direction specifies whether to list imported (INCOMING) or exported (OUTGOING) routes.

Deleting a VPC Network Peering connection

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

Console

  1. Go to the VPC Network Peering page in the Google Cloud Platform Console.
    Go to the VPC Network Peering page
  2. Select the checkbox next to the peering you want to remove.
  3. Click Delete.

gcloud 

gcloud compute networks peerings delete [PEERING-NAME] \
    --network [NETWORK-NAME]

Example VPC Network Peering setup

Consider an organization organization-a which needs VPC Network Peering to be established between network-a in project-a and network-b in project-b. In order for VPC Network Peering to be established successfully, administrators of network-a and network-b must separately configure the peering association.

Step 1: Peer network-a with network-b

A user with appropriate IAM permissions in project-a configures network-a to peer with network-b. For example, users with the roles/editor or roles/compute.networkAdmin role can configure peering.

Peering from network-a to network-b
Peering from network-a to network-b (click to enlarge)

Before you begin, you will need the project IDs and network names of the networks you want to peer.

Console

  1. Go to the VPC Network Peering page in the Google Cloud Platform Console.
    Go to the VPC Network Peering page
  2. Click Create connection.
  3. Click Continue.
  4. Enter a Name of peer-ab for this side of the connection.
  5. Under Your VPC network, select the network you want to peer.
  6. Set the Peering VPC network radio buttons to In another project, unless you wish to peer within the same project.
  7. Specify the Project ID of the other project.
  8. Specify VPC network name of the other network.
  9. Click Create.
  10. Import and export custom routes.
    1. Expand the Custom routes section.
    2. Select Import custom routes and Export custom routes

gcloud 

gcloud beta compute networks peerings create peer-ab \
    --network network-a \
    --peer-project project-b \
    --peer-network network-b \
    --import-custom-routes \
    --export-custom-routes

At this point, the peering state remains INACTIVE because there is no matching configuration in network-b in project-b.

When the peering state becomes ACTIVE, VPC Network Peering automatically exchanges subnet routes. GCP also exchanges custom routes (static routes and dynamic routes) by importing or exporting them over the peering connection. Both networks must be configured to exchange custom routes before they are shared. For more information, see Importing and exporting custom routes.

To see the current peering state, view the peering connection:

Console

  1. Go to the VPC Network Peering page in the Google Cloud Platform Console.
    Go to the VPC Network Peering page
  2. Status says "Waiting for peer network to connect."

gcloud 

gcloud compute networks peerings list --network network-a

NAME      NETWORK   PEER_PROJECT PEER_NETWORK AUTO_CREATE_ROUTES   IMPORT_CUSTOM_ROUTES EXPORT_CUSTOM_ROUTES STATE    STATE_DETAILS
peer-ab   network-b project-b    network-b    True                 True                 True                 INACTIVE The peering network has not been configured.

Step 2: Peer network-b with network-a

A NetworkAdmin, or a user with appropriate IAM permissions, in project-b must configure the matching configuration from network-b to network-a in order for the peering to become ACTIVE on both ends.

Peering from network-b to network-a (click to enlarge)
Peering from network-a to network-b (click to enlarge)

Console

  1. Go to the VPC Network Peering page in the Google Cloud Platform Console.
    Go to the VPC Network Peering page
  2. Click Create connection.
  3. Click Continue.
  4. Enter a Name of peer-ba for this side of the connection.
  5. Under Your VPC network, select the network you want to peer.
  6. Set the Peering VPC network radio buttons to In another project, unless you wish to peer within the same project.
  7. Specify the Project ID of the other project.
  8. Specify VPC network name of the other network.
  9. Click Create.
  10. Import and export custom routes.
    1. Expand the Custom routes section.
    2. Select Import custom routes and Export custom routes

gcloud 

gcloud beta compute networks peerings create peer-ba \
     --network network-b \
     --peer-project project-a \
     --peer-network network-a \
     --import-custom-routes \
     --export-custom-routes

Step 3: VPC Network Peering becomes ACTIVE

As soon as the peering moves to an ACTIVE state, subnet routes and custom routes are exchanged. The following traffic flows are set up:

  • Between VM instances in the peered networks: Full mesh connectivity.
  • From VM instances in one network to Internal Load Balancing endpoints in the peered network
Peering ACTIVE (click to enlarge)
Peering ACTIVE (click to enlarge)

Console

  1. Go to the VPC Network Peering page in the Google Cloud Platform Console.
    Go to the VPC Network Peering page
  2. Status says "Connected."
  3. Go to the VPC Network Peering page in the other project to see that it also says "Connected."

gcloud 

gcloud compute networks peerings list --network network-a

NAME      NETWORK   PEER_PROJECT PEER_NETWORK AUTO_CREATE_ROUTES   IMPORT_CUSTOM_ROUTES EXPORT_CUSTOM_ROUTES STATE    STATE_DETAILS
peer-ab  network-a   project-b    network-b   True                 True                 True                 ACTIVE   The peering became ACTIVE at 2016-06-08T15:10:14.111-07:00.

gcloud compute networks peerings list --network network-b

NAME      NETWORK   PEER_PROJECT PEER_NETWORK AUTO_CREATE_ROUTES   IMPORT_CUSTOM_ROUTES EXPORT_CUSTOM_ROUTES STATE    STATE_DETAILS
peer-ba  network-b   project-a    network-a   True                 True                 True                 ACTIVE   The peering became ACTIVE at 2016-06-08T15:10:14.111-07:00.

The routes to peered network CIDR prefixes are now visible across the VPC network peers. These routes are implicit routes that generated for active peering connections. They don't have corresponding route resources. The following procedure shows routes for all VPC networks for project-a.

Console

  1. Go to the Routes page in the Google Cloud Platform Console.
    Go to the Routes page

gcloud 

gcloud compute routes list --project project-a

NAME                              NETWORK    DEST_RANGE     NEXT_HOP                  PRIORITY
default-route-2a865a00fa31d5df    network-a  0.0.0.0/0      default-internet-gateway  1000
default-route-8af4732e693eae27    network-a  10.0.0.0/16                              1000
peering-route-4732ee69e3ecab41    network-a  10.8.0.0/16    peer-ab                   1000
peering-static-route              network-a  10.138.0.0/20  peer-ab                   1000

Creating multiple peering connections

Consider the scenario in which VM instances in network-a need to access services from two different external organizations: SaaS1 and SaaS2. To access both using only internal (private, RFC 1918) IP addresses, two peering connections are required:

  • network-a peers with network-b, which is in SaaS1
  • network-a peers with network-c, which is in SaaS2

With VPC Network Peering, it doesn't matter that that network-b and network-c are in different projects and different organizations.

Cross-organization peering (click to enlarge)
Cross-organization peering (click to enlarge)

To create this setup, simply create two different peering sessions.

Restrictions

No subnet IP range overlap across peered VPC networks

No subnet IP range can overlap with another subnet IP range in a peered VPC network.

Checks performed at VPC Network Peering setup

At the time of peering, GCP checks to see if there are any subnets with overlapping IP ranges between the two VPC networks or any of their peered networks. If there is an overlap, peering is not established. Since a full mesh connectivity is created between VM instances, subnets in the peered VPC networks can’t have overlapping IP ranges as this would cause routing issues.

Overlapping subnet IP ranges between two peers (click to enlarge)
Overlapping subnet IP ranges between two peers (click to enlarge)

If there were any subnets with overlapping IP ranges between peers of a given VPC network, it would cause a routing conflict. For example, suppose VPC network N1 has already peered with VPC network N2, then VPC network N3 tries to peer with N2. This is an invalid peering because N3 has a subnet Subnet_5 whose IP range overlaps with Subnet_1 in network N1.

Overlapping subnet IP ranges with three peers (click to enlarge)
Overlapping subnet IP ranges with three peers (click to enlarge)

Checks performed at subnet creation in VPC Network Peering scenarios

When a VPC subnet is created or a subnet IP range is expanded, GCP performs a check to make sure the new subnet range does not overlap with IP ranges of subnets in the same VPC network or in directly peered VPC networks. If it does, the creation or expansion action fails. For example, when a new subnet subnet_3 is created in network N2 in the following figure, the IP ranges must not overlap with the IP ranges defined in the directly peered network N1.

Subnet creation check (click to enlarge)
Subnet creation check (click to enlarge)

GCP also ensures that no overlapping subnet IP ranges are allowed across VPC networks that have a peered network in common. If it does, the creation or expansion action fails. For example, when a new subnet subnet_5 is created in network N3 in the following figure, the IP ranges must not overlap with the IP ranges defined in directly peered network N2, or with network N1, because N1 is already peered with N2.

Subnet creation check with three peers (click to enlarge)
Subnet creation check with three peers (click to enlarge)

Legacy networks are not supported in VPC Network Peering

Legacy Networks are networks that do not have subnets. Legacy networks cannot peer with any other networks and are not supported in VPC Network Peering.

No Compute Engine DNS across projects

Compute Engine internal DNS names created in a network are not accessible to peered networks. The IP address of the VM should be used to reach the VM instances in peered network.

Tags and service accounts are not usable across peered networks

You cannot use a tag or service account from one peered network in the other peered network.

GKE with VPC Network Peering

VPC Network Peering with GKE is supported when used with IP Aliases and custom routes. Kubernetes Services, if exposed via Internal Load Balancing, and Pod IPs are reachable across VPC networks.

Limits

See VPC Network Peering limits.

Troubleshooting

Q: My peering connection is set up, but I am not able to reach peer VMs or internal load balancers.

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 VPC networks. This time depends on the size of the VPC networks that are peering. If you have just set up the peering connection, please 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.

Q: When I try to set up the peering connection, I get an error that another peering operation is in progress.

In order to avoid contention with routing updates and the like, GCP 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, all the tasks from the first peering may not have completed. It may take up to a minute for all tasks to complete. Alternatively, your existing network peer may be adding an internal load balancer or VM, both of which affect what is reachable between networks. In most cases, you should wait a minute or two and retry the peering operation.

Q: When I try to delete a VPC network with ACTIVE peerings, I get an error.

Before you can delete a VPC network, you must first delete all peering configurations in the network. See deleting a VPC network peering connection.

Q: Can you peer VPC networks that have subnets with overlapping primary or secondary IP ranges?

No. You can only peer VPC networks whose subnets have unique primary and secondary subnet IP ranges.

Q: How do I make sure new subnets I create in my VPC network will not have subnet IP ranges that conflict with subnets or routes in peer networks?

Before creating new subnets, you can list the routes from peering connections. Make sure you do not use any of their destinations as either primary or secondary IP ranges when you create new subnets in your VPC network.

Q: I have a VPC network that is peered with another VPC network. I want to create a subnet in my VPC network. How do I create this subnet so that it does not overlap with my peer's peer subnets?

At this time, there is no command that helps you to find this. Please ask the admin of the peered network to find out what subnet routes are already in that network.

Q: Are there any security or privacy concerns with VPC peering?

After peering is set up, each VPC network knows the subnet ranges of the other network. In addition, each peer VPC network is able to send and receive traffic from the all VMs in the other network unless firewall rules are in place to prevent it. Other than that, peered networks do not have visibility into each other.

Q: How do I determine if there are any requests from other VPC networks to connect to my VPC network using VPC Network Peering?

There is no way to list any peering requests for your VPC network. You can only see the peering configurations that you have created.

VPC Network Peering requires that both your network and another network create a peering configuration to one another before a connection can be established. Even if a network administrator for another VPC network creates a peering configuration to your network, no peering connection will be created unless you create a peering configuration to that network.

Q: How do I make routes in a peer network available to an on-premises network connected to my VPC network using Cloud VPN or Cloud Interconnect?

VPC Network Peering does not support transitive routing; that is, imported routes from other networks are not automatically advertised by Cloud Routers in your VPC network. However, you can use custom IP range advertisements from Cloud Routers in your VPC network to share routes to destinations in the peer network.

For Cloud VPN tunnels using static routing, you must configure static routes to the peer network's destination ranges in your on-premises network.

Q: Why are custom routes not exchanged between peered networks?

First, list the routes from your peering connections. If you don't see routes to destinations that you expect, check the following:

  • List peering connections. Find the network with the desired destination ranges, and ensure that its peering state is ACTIVE. If the peering connection is INACTIVE, a peering configuration for your network does not exist in the other network. If you don't manage the other network, you'll need to coordinate with a network administrator who does.

  • Update the peering configuration in your network so that it is configured to import custom routes from the other network. Ensure that the other network has been configured to export its custom routes.

Q: Why is traffic destined for a peer network being dropped?

First, list peering connections to make sure your network is still connected to the other one. If the peering state is INACTIVE, a peering configuration for your network does not exist in the other network. If you don't manage the other network, you'll need to contact a network administrator who does.

Next, list routes from peer connections. You can only import as many routes as are allowed by the VPC Network Peering limits.

Q: Why is traffic being sent to an unexpected next hop?

Review the routing order to see if another route was chosen instead.

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