Local VCN Peering using Local Peering Gateways

Local VCN peering is the process of connecting two VCNs in the same region so that their resources can 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.

See Gateway Limits and Requesting a Service Limit Increase for limits-related information.

For more information, see Access to Other VCNs: Peering.

Summary of Networking Components for Peering using an LPG

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

• Two VCNs with non-overlapping CIDRs, in the same region
• A local peering gateway (LPG) on each VCN in the peering relationship.
• A connection between those two LPGs.
• 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.

Note

A given VCN can use the peered LPGs to reach these resources:

• VNICs in the other VCN
• An on-premises network attached to the other VCN, if an advanced routing scenario called transit routing has been set up for the VCNs

A VCN can't use its peered VCN to reach other destinations outside of the VCNs (such as the internet). 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. However, VCN-2 could receive traffic from the internet by way of VCN-1. For more information, see Important Implications of VCN Peering.

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

PEERING

A peering is a single peering relationship between two VCNs. Example: If VCN-1 peers with three other VCNs, then there are three peerings. The local part of local peering indicates that the VCNs are in the same region. A given VCN can have a maximum of 10 local peerings at a time.

Caution

The two VCNs in the peering relationship must not have overlapping CIDRs. However, if VCN-1 is peered with three other VCNs, those three VCNs can have overlapping CIDRs with each other. You would set up the subnets in VCN-1 to have route rules that direct traffic to the targeted peered VCN.

VCN ADMINISTRATORS

In general, VCN peering can occur only if both of the VCN administrators agree to it. In practice, this means that 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.

For more information about the required policies and VCN configuration, see Setting Up a Local Peering.

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 LPGs. In turn, the acceptor must create a particular IAM policy that gives the requestor permission to connect to LPGs in the acceptor's compartment . Without that policy, the requestor's request to connect fails.

LOCAL PEERING GATEWAY (LPG)

A local peering gateway (LPG) is a component on a VCN for routing traffic to a locally peered VCN. As part of configuring the VCNs, each administrator must create an LPG for their VCN. A given VCN must have a separate LPG for each local peering it establishes (maximum 10 LPGs per VCN). To continue with the previous example: VCN-1 would have three LPGs to peer with three other VCNs. In the API, a LocalPeeringGateway is an object that contains information about the peering. You can't reuse an LPG to later establish another peering.

PEERING CONNECTION

When the requestor initiates the request to peer (in the Console or API), they're effectively asking to connect the two LPGs. The requestor must have information to identify each LPG (such as the LPG's compartment and name, or the LPG's OCID). Each administrator must put the required IAM policies in place for their compartment or tenancy.

Either VCN administrator can terminate a peering by deleting their LPG. In that case, the other LPG's status switches to REVOKED. The administrator could instead render the connection non-functional by removing the route rules or security rules that enable traffic to flow across the connection (see the next sections).

ROUTING TO THE LPG

As part of configuring the VCNs, each administrator must update the VCN's routing to enable traffic to flow between the VCNs. In practice, this looks just like routing you set up for any gateway (such as an internet gateway or dynamic routing gateway). 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 LPG as the target. Your LPG routes traffic that matches that rule to the other LPG, 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) that is destined for an instance in VCN-2 (192.168.0.15) is routed to LPG-1 based on the rule in Subnet A's route table (see Callout 1: Subnet A Route Table). From there the traffic is routed to LPG-2, and then from there, on to its destination in Subnet X.

Callout 1: Subnet A Route Table

Destination CIDR	Route Target
0.0.0.0/0	Internet Gateway
172.16.0.0/12	DRG
192.168.0.0/16	LPG-1

Callout 2: Subnet X Route Table

Destination CIDR	Route Target
10.0.0.0/16	LPG-2

Note

As mentioned earlier, a given VCN can use the peered LPGs to reach VNICs in the other VCN, or the on-premises network if transit routing is set up for the VCNs. But a VCN can't use the peered VCN to reach other destinations outside of the VCNs (such as 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 have the option to 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.

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

Here's the general process for setting up a peering between two VCNs in the same region:

1. Create the LPGs: Each VCN administrator creates an LPG for their own VCN.
2. Share information: The administrators share the basic required information.
3. Set up the required IAM policies for the connection: The administrators set up IAM policies to enable the connection to be established.
4. Establish the connection: The requestor connects the two LPGs.
5. Update route tables: Each administrator updates their VCN's route tables to enable traffic between the peered VCNs as wanted.
6. Update security rules: Each administrator updates their VCN's security rules to enable traffic between the peered VCNs as wanted.

If wanted, the administrators can perform tasks E and F before establishing the connection. In that case, each administrator must know the CIDR block or specific subnets from the other's VCN and share that in task B. After the connection is established, you can also get the CIDR block of the other VCN by viewing your own LPG's details in the Console. Look for Peer Advertised CIDR. Or if you're using the API, see the peerAdvertisedCidr parameter.

You will also need to pre-configure some IAM settings like groups prior to going through the step-by-step process.