Remote VCN Peering through an Upgraded DRG

This topic is about remote VCN peering.

In this case, remote means that the virtual cloud networks (VCNs) are each attached to a different dynamic routing gateway  (DRG) that resides in a different region. If the VCNs you want to connect are in the same region, see Local VCN Peering Through an Upgraded DRG.

Note

This scenario is available to an upgraded or legacy DRG, with the exception that a legacy DRGs will not support connecting DRGs in different tenancies. See DRG versions for a breakdown on the possible versions of DRG.

Before you attempt to implement this scenario, ensure that:

  • VCN A is attached to DRG A in region 1
  • VCN B is attached to DRG B in region 2
  • Routing configuration in both DRGs is unchanged
  • Appropriate IAM permissions are applied for VCNs that are either in the same or different tenancies

Overview of Remote VCN Peering

Remote VCN peering is the process of connecting two VCNs in different regions. The peering allows the VCNs' resources to communicate using private IP addresses without routing the traffic over the internet or through your on-premises network. The VCNs can be in the same Oracle Cloud Infrastructure tenancy  or different ones. Without peering, a given VCN would need an internet gateway and public IP addresses for the instances that need to communicate with another VCN in a different region.

Summary of Networking Components for Remote Peering

At a high level, the Networking service components required for a remote peering include:

  • Two VCNs with non-overlapping CIDRs, in different regions.

    Note

    No VCN CIDRs can overlap

    The two VCNs in the peering relationship cannot have overlapping CIDRs. Also, if a particular VCN has multiple peering relationships, those other VCNs must not have overlapping CIDRs with each other. For example, if VCN-1 is peered with VCN-2 and also VCN-3, then VCN-2 and VCN-3 must not have overlapping CIDRs.

    If you are configuring this scenario, you have to meet this requirement in the planning stage. Routing problems are likely when overlapping CIDRs occur, but you aren't prevented by the Console or API operations from creating a configuration that causes issues.

  • A Dynamic Routing Gateway (DRG) attached to each VCN in the peering relationship. Your VCN already has a DRG if you're using a Site-to-Site VPN IPSec tunnel or an Oracle Cloud Infrastructure FastConnect private virtual circuit.
  • A remote peering connection (RPC) on each DRG in the peering relationship.
  • A connection between those two RPCs.
  • Supporting route rules to enable traffic to flow over the connection, and only to and from select subnets in the respective VCNs (if wanted).
  • Supporting security rules to control the types of traffic allowed to and from the instances in the subnets that need to communicate with the other VCN.

The following diagram illustrates the components.

This image shows the basic layout of two VCNs that are remotely peered, each with a remote peering connection on the DRG
Note

A given VCN can use the connected RPCs to reach only VNICs in the other VCN, or your on-premises network if the DRG has a connection to an on-premises CPE. For example, if VCN-1 in the preceding diagram were to have an internet gateway, the instances in VCN-2 could NOT use it to send traffic to endpoints on the internet. For more information, see Important Implications of Peering.

Important Implications of Peering

If you haven't yet, read Important Implications of Peering to understand important access control, security, and performance implications for peered VCNs.

Peering VCNs in different tenancies has some permissions complications that need to be resolved in both tenancies. See IAM Policies for Routing Between VCNs for details on the permissions needed.

Spoke-to-Spoke: Remote Peering with Transit Routing (Legacy DRGs Only)

Note

The scenario this section mentions is still supported, but Oracle recommends you use the DRG transit routing method described in Routing traffic through a central network virtual appliance.

Imagine that in each region you have multiple VCNs in a hub-and-spoke layout, as shown in the following diagram. This type of layout within a region is discussed in detail in Transit Routing inside a hub VCN. The spoke VCNs in a given region are locally peered with the hub VCN in the same region, using local peering gateways .

You can set up remote peering between the two hub VCNs. You can then also set up transit routing for the hub VCN's DRG and LPGs, as discussed in Transit Routing inside a hub VCN. This setup allows a spoke VCN in one region to communicate with one or more spoke VCNs in the other region without needing a remote peering connection directly between those VCNs.

For example, you could configure routing so that resources in VCN-1-A could communicate with resources in VCN-2-A and VCN-2-B by way of the hub VCNs. That way, VCN 1-A is not required to have a separate remote peering with each of the spoke VCNs in the other region. You could also set up routing so that VCN-1-B could communicate with the spoke VCNs in region 2, without needing its own remote peerings to them.

This image shows the basic layout of two regions with VCNs in a hub-and-spoke layout, with remote peering between the hub VCNs.

Spoke-to-Spoke: Remote Peering with Transit Routing (Upgraded DRG)

Note

The scenario this section uses the DRG transit routing method described in Routing traffic through a central network virtual appliance.

Imagine that in each region you have multiple VCNs in a hub-and-spoke layout, as shown in the following diagram. This type of layout within a region is discussed in detail in Transit Routing inside a hub VCN. The spoke VCNs in a given region are locally peered with the hub DRG/VCN pair in the same region by mutual connection to the DRG.

You can set up remote peering between the two hub VCNs. You can then also set up transit routing for the hub VCN's DRG, as discussed in Routing traffic through a central network virtual appliance. This setup allows a spoke VCN in one region to communicate with one or more spoke VCNs in the other region without needing a remote peering connection directly between those VCNs.

For example, you could configure routing so that resources in VCN-1-A could communicate with resources in VCN-2-A and VCN-2-B by way of the hub VCNs. That way, VCN 1-A is not required to have a separate remote peering with each of the spoke VCNs in the other region. You could also set up routing so that VCN-1-B could communicate with the spoke VCNs in region 2, without needing its own remote peerings to them.

This image shows the basic layout of two regions with VCNs in a hub-and-spoke layout, with remote peering between the hub VCNs.

Important Remote Peering Concepts

The following concepts help you understand the basics of VCN peering and how to establish a remote peering.

PEERING
A peering is a single peering relationship between two VCNs. Example: If VCN-1 peers with two other VCNs, two peerings exist. The remote part of remote peering indicates that the VCNs are in different regions. For this method of remote peering, the VCNs can be in the same tenancy or in different tenancies.
VCN ADMINISTRATORS
In general, VCN peering can occur only if both of the VCN administrators agree to it. In practice, the two administrators must:
  • Share some basic information with each other.
  • Coordinate to set up the required Oracle Cloud Infrastructure Identity and Access Management policies to enable the peering.
  • Configure their VCNs for the peering.
Depending on the situation, a single administrator might be responsible for both VCNs and the related policies. The VCNs can be in the same tenancy or in different tenancies.
For more information about the required policies and VCN configuration, see IAM Policies for Routing Between VCNs.
ACCEPTOR AND REQUESTOR
To implement the IAM policies required for peering, the two VCN administrators must designate one administrator as the requestor and the other as the acceptor. The requestor must be the one to initiate the request to connect the two RPCs. In turn, the acceptor must create a particular IAM policy that gives the requestor permission to connect to RPCs in the acceptor's compartment . Without that policy, the requestor's request to connect fails.
REGION SUBSCRIPTION
To peer with a VCN in another region, your tenancy must first be subscribed to that region. For information about subscribing, see Managing Regions.
REMOTE PEERING CONNECTION (RPC)
A remote peering connection (RPC) is a component you create on the DRG attached to your VCN. The RPC's job is to act as a connection point for a remotely peered VCN. As part of configuring the VCNs, each administrator must create an RPC for the DRG on their VCN. A given DRG must have a separate RPC for each remote peering it establishes for the VCN. To continue with the previous example: the DRG on VCN-1 would have two RPCs to peer with two other VCNs. In the API, a RemotePeeringConnection is an object that contains information about the peering. You can't reuse an RPC to later establish another peering with it.
CONNECTION BETWEEN TWO RPCS
When the requestor initiates the request to peer (in the Console or API), they're effectively asking to connect the two RPCs. The requestor must have information to identify each RPC (such as the RPC's region and OCID ).
Either VCN administrator can terminate a peering by deleting their RPC. In that case, the other RPC's status switches to REVOKED. The administrator could instead render the connection non-functional by removing the route rules that enable traffic to flow across the connection (see the next section).
ROUTING TO THE DRG
As part of configuring the VCNs, each administrator must update the VCN's routing to enable traffic to flow between the VCNs. For each subnet that needs to communicate with the other VCN, you update the subnet's route table. The route rule specifies the destination traffic's CIDR and your DRG as the target. Your DRG routes traffic that matches that rule to the other DRG, which in turn routes the traffic to the next hop in the other VCN.
In the following diagram, VCN-1 and VCN-2 are peered. Traffic from an instance in Subnet A (10.0.0.15) destined for an instance in VCN-2 (192.168.0.15) is routed to DRG-1 based on the rule in Subnet A's route table. From there the traffic is routed through the RPCs to DRG-2, and then from there, on to the destination in Subnet X.
This image shows the route tables and path of traffic routed from one DRG to the other.
Callout 1: Subnet A Route Table
Destination CIDR Route Target
0.0.0.0/0 Internet Gateway
192.168.0.0/16 DRG-1
Callout 2: Subnet X Route Table
Destination CIDR Route Target
10.0.0.0/16 DRG-2
Note

As mentioned earlier, a given VCN can use the connected RPCs to reach only VNICs in the other VCN or your on-premises network, and not destinations on the internet. For example, in the preceding diagram, VCN-2 cannot use the internet gateway attached to VCN-1.

SECURITY RULES
Each subnet in a VCN has one or more security lists that control traffic in and out of the subnet's VNICs at the packet level. You can use security lists to control the type of traffic allowed with the other VCN. As part of configuring the VCNs, each administrator must determine which subnets in their own VCN need to communicate with VNICs in the other VCN and update their subnet's security lists accordingly.
If you use network security groups (NSGs) to implement security rules, notice that you can write security rules for an NSG that specify another NSG as the source or destination of traffic. However, the two NSGs must belong to the same VCN.

Important Implications of Peering

If you haven't yet, read Important Implications of Peering to understand important access control, security, and performance implications for peered VCNs.

Setting Up a Remote Peering

This section covers the general process for setting up a peering between two VCNs in different regions.

Important

The following procedure assumes that:

Overview of required steps:

  1. Create the RPCs: Each VCN administrator creates an RPC for their own VCN's DRG.
  2. Share information: The administrators share the basic required information.
  3. Establish the connection: The requestor connects the two RPCs (see Important Remote Peering Concepts for the definition of the requestor and acceptor).
  4. Update route tables: Each administrator updates their VCN's route tables to enable traffic between the peered VCNs as intended.
  5. Update security rules: Each administrator updates their VCN's security rules to enable traffic between the peered VCNs as intended.

If you want, the administrators can perform tasks 4 and 5 before establishing the connection. Each administrator needs to know the CIDR block or specific subnets from the other's VCN and share that in task 2.

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