Unsupported VPC Peering Configurations
Scenarios
Scenario |
Example |
---|---|
|
|
VPC peering connections cannot enable ECSs in their VPCs to share an EIP to access the Internet. If VPC-A and VPC-B are peered and ECS-A01 in VPC-A has an EIP, ECS-B01 in VPC-B cannot access the Internet using the EIP bound to ECS-A01. |
Invalid VPC Peering for Overlapping VPC CIDR Blocks
- VPCs with the same CIDR block also include subnets that overlap.
VPC peering connections are not usable. As shown in Table 2, VPC-A and VPC-B, and their subnets have the same CIDR block. If you create a VPC peering connection between VPC-A and VPC-B, their route tables are shown in Table 2.
In the rtb-VPC-A route table, the custom route for routing traffic from VPC-A to VPC-B and the local route have overlapping destinations. The local route has a higher priority and traffic will be forwarded within VPC-A and cannot reach VPC-B.Figure 1 Networking diagram (IPv4)
Table 2 VPC route table details Route Table
Destination
Next Hop
Route Type
Description
rtb-VPC-A
10.0.0.0/24
Local
System
Local routes are automatically added for communications within a VPC.
10.0.1.0/24
Local
System
10.0.0.0/16 (VPC-B)
Peering-AB
Custom
Add a route with the CIDR block of VPC-B as the destination and Peering-AB as the next hop.
rtb-VPC-B
10.0.0.0/24
Local
System
Local routes are automatically added for communications within a VPC.
10.0.1.0/24
Local
System
10.0.0.0/16 (VPC-A)
Peering-AB
Custom
Add a route with the CIDR block of VPC-A as the destination and Peering-AB as the next hop.
If two VPCs want to use their IPv6 CIDR blocks for communication by a VPC peering connection but the IPv4 CIDR blocks of the VPCs or subnets overlap, the connection is not usable.
Figure 2 Networking diagram (IPv6)
- Two VPCs have overlapping CIDR blocks but some of their subnets do not overlap.
VPC peering connections will not take effect in the following scenarios:
- Connecting overlapping CIDR blocks of VPCs
As shown in Figure 3, if you create a VPC peering connection between VPC-A and VPC-B, the VPC peering connection will not take effect because the two VPCs have the same CIDR block.
- Connecting overlapping subnets from different VPCs
If you create a VPC peering connection between Subnet-A01 and Subnet-B02, the route tables are shown in Table 3. In the rtb-VPC-B route table, the custom route for routing traffic from Subnet-B02 to Subnet-A01 and the local route have overlapping destinations. The local route has a higher priority and traffic will be forwarded within Subnet-B02 and cannot reach Subnet-A01.
Table 3 VPC route table details Route Table
Destination
Next Hop
Route Type
Description
rtb-VPC-A
10.0.0.0/24
Local
System
Local routes are automatically added for communications within a VPC.
10.0.1.0/24
Local
System
10.0.2.0/24 (Subnet-B02)
Peering-AB
Custom
Add a route with the CIDR block of Subnet-B02 as the destination and Peering-AB as the next hop.
rtb-VPC-B
10.0.0.0/24
Local
System
Local routes are automatically added for communications within a VPC.
10.0.2.0/24
Local
System
10.0.0.0/24 (Subnet-A01)
Peering-AB
Custom
Add a route with the CIDR block of Subnet-A01 as the destination and Peering-AB as the next hop.
If the subnets connected by a VPC peering connection do not overlap, the connection will take effect. As shown in Figure 4, you can create a VPC peering connection between Subnet-A02 and Subnet-B02. In this case, the routes do not conflict and the VPC peering connection takes effect.If two VPCs want to use their IPv6 CIDR blocks for communication by a VPC peering connection but the IPv4 CIDR blocks of the VPCs or subnets overlap, the connection is not usable.
Figure 5 Networking diagram (IPv6)
- Connecting overlapping CIDR blocks of VPCs
Invalid VPC Peering for Sharing an EIP
As shown in Figure 6, although VPC-A and VPC-B are peered and ECS-A01 in VPC-A has an EIP, ECS-B01 in VPC-B cannot access the Internet using the EIP bound to ECS-A01.
Feedback
Was this page helpful?
Provide feedbackThank you very much for your feedback. We will continue working to improve the documentation.