Updated on 2024-09-18 GMT+08:00

Step 1: Plan Networks and Resources

To use an enterprise router to connect VPCs in the same region, you need to:
  • Network Planning: Plan CIDR blocks of VPCs and subnets, and route tables of VPCs and the enterprise router.
  • Resource Planning: Plan the quantity, names, and parameters of cloud resources, including VPCs, ECSs, and the enterprise router.

Network Planning

Figure 1 and Table 2 show the network planning and its description for communications among VPCs in the same region.

Figure 1 Network planning for communications among VPCs in the same region
Table 1 Network traffic flows

Scenario

Description

Request from VPC 1 to VPC 3

  1. The route table of VPC 1 has a route with next hop set to the enterprise router to forward traffic from VPC 1 to the enterprise router.
  2. The route table of the enterprise router has a propagated route with next hop set to the VPC 3 attachment to forward traffic from the enterprise router to VPC 3.

Response from VPC 3 to VPC 1

  1. The route table of VPC 3 has a route with next hop set to the enterprise router to forward traffic from VPC 3 to the enterprise router.
  2. The route table of the enterprise router has a propagated route with next hop set to the VPC 1 attachment to forward traffic from the enterprise router to VPC 1.
Table 2 Network planning for communications among VPCs in the same region

Resource

Description

VPC

  • The CIDR blocks of the VPCs to be connected cannot overlap with each other.

    In this example, the CIDR blocks of the VPCs are propagated to the enterprise router route table as the destination in routes. The CIDR blocks cannot be modified and overlapping CIDR blocks may cause route conflicts.

    If your existing VPCs have overlapping CIDR blocks, do not use propagated routes. Instead, you need to manually add static routes to the route table of the enterprise router. The destination can be VPC subnet CIDR blocks or smaller ones.

  • Each VPC has a default route table.
  • Routes in the default route table can be:
    • Local: a system route for communications between subnets in a VPC.
    • Enterprise router: custom routes with 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16 as the destinations for routing traffic from a VPC subnet to the enterprise router. See Table 3 for route details.

Enterprise router

After Default Route Table Association and Default Route Table Propagation are enabled and a VPC attachment is created, the system will automatically:
  • Associate VPC attachments with the default route table of the enterprise router.
  • Propagate VPC attachments with the default route table of the enterprise router. The route table automatically learns the VPC CIDR block as the destination of routes. For details, see Table 4.

ECS

The four ECSs are in different VPCs. If the ECSs are associated with different security groups, add rules to their security groups to allow access to each other.

Table 3 VPC route table

Destination

Next Hop

Route Type

10.0.0.0/8

Enterprise router

Static route (custom)

172.16.0.0/12

Enterprise Router

Static route (custom)

192.168.0.0/16

Enterprise Router

Static route (custom)

  • If you enable Auto Add Routes when creating a VPC attachment, you do not need to manually add static routes to the VPC route table. Instead, the system automatically adds routes (with this enterprise router as the next hop and 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16 as the destinations) to all route tables of the VPC.
  • If an existing route in the VPC route tables has a destination to 10.0.0.0/8, 172.16.0.0/12, or 192.168.0.0/16, the routes will fail to be added. In this case, do not enable Auto Add Routes. After the attachment is created, manually add routes.
  • Do not set the destination of a route (with an enterprise router as the next hop) to 0.0.0.0/0 in the VPC route table. If an ECS in the VPC has an EIP bound, the VPC route table will have a policy-based route with 0.0.0.0/0 as the destination, which has a higher priority than the route with the enterprise router as the next hop. In this case, traffic is forwarded to the EIP and cannot reach the enterprise router.
Table 4 Enterprise router route table

Destination

Next Hop

Route Type

VPC 1 CIDR block: 192.168.0.0/16

VPC 1 attachment: er-attach-01

Propagated route

VPC 2 CIDR block: 172.16.0.0/16

VPC 2 attachment: er-attach-02

Propagated route

VPC 3 CIDR block: 10.1.0.0/16

VPC 3 attachment: er-attach-03

Propagated route

VPC 4 CIDR block: 10.2.0.0/16

VPC 4 attachment: er-attach-04

Propagated route

Resource Planning

The enterprise router, VPCs, and ECSs must be in the same region. You can select any AZ within the region.

The following resource details are only examples. You can modify them as required.

  • One enterprise router
    Table 5 Enterprise router details

    Enterprise Router Name

    ASN

    Default Route Table Association

    Default Route Table Propagation

    Association Route Table

    Propagation Route Table

    Attachment

    er-test-01

    64512

    Enable

    Enable

    Default route table

    Default route table

    er-attach-01

    er-attach-02

    er-attach-03

    er-attach-04

  • Four VPCs, each with a unique CIDR block
    Table 6 VPC details

    VPC Name

    VPC CIDR Block

    Subnet Name

    Subnet CIDR Block

    Association Route Table

    vpc-demo-01

    192.168.0.0/16

    subnet-demo-01

    192.168.1.0/24

    Default route table

    vpc-demo-02

    172.16.0.0/16

    subnet-demo-02

    172.16.1.0/24

    Default route table

    vpc-demo-03

    10.1.0.0/16

    subnet-demo-03

    10.1.1.0/24

    Default route table

    vpc-demo-04

    10.2.0.0/16

    subnet-demo-04

    10.2.1.0/24

    Default route table

  • An ECS in each VPC, a total of four ECSs
    Table 7 ECS details

    ECS

    Image

    VPC

    Subnet

    Security Group

    Private IP Address

    ecs-demo-01

    Public image:

    EulerOS 2.5 6

    vpc-demo-01

    subnet-demo-01

    sg-demo (general-purpose web server)

    192.168.1.12

    ecs-demo-02

    vpc-demo-02

    subnet-demo-02

    172.16.1.189

    ecs-demo-03

    vpc-demo-03

    subnet-demo-03

    10.1.1.105

    ecs-demo-04

    vpc-demo-04

    subnet-demo-04

    10.2.1.83