Question

You have successfully set up a VPC peering connection in your account between two VPCs – VPC A and VPC B, each in a different region. When you are trying to make a request from VPC A to VPC B, the request fails. Which of the following could be a reason?

A. Cross-region peering is not supported in AWS

B. CIDR blocks of both VPCs might be overlapping.

C. Routes not configured in route tables for peering connections.

D. VPC A security group default outbound rules not allowing traffic to VPC B IP range.

Answer 1

C. Routes not configured in route tables for peering connections.

Option A is not correct. Cross-region VPC peering is supported in AWS.

Option B is not correct.

When the VPC IP CIDR blocks are overlapping, you cannot create a peering connection. Question states the peering connection was successful.

Option C is correct.

To send private IPv4 traffic from your instance to an instance in a peer VPC, you must add a route to the route table that’s associated with your subnet in which your instance resides. The route points to the CIDR block (or portion of the CIDR block) of the peer VPC in the VPC peering connection.

https://docs.aws.amazon.com/AmazonVPC/latest/PeeringGuide/vpc-peering-routing.html

Option D is not correct.

A security group’s default outbound rule allows all traffic to go out from the resources attached to the security group.