Question

A SysOps administrator is asked to establish a VPC peering connection between two VPCs owned by the same account so that application servers in each VPC can communicate over private IPs. VPC-A uses the CIDR block 10.0.0.0/16 and VPC-B uses 10.0.0.0/16 as well. When the administrator attempts to create the peering connection, it cannot be established, or once created, routing does not work. What is the root cause and the appropriate resolution?

Accepted Answer

VPC peering does not support overlapping CIDR blocks; one VPC must be recreated or migrated to a non-overlapping CIDR range before peering will function.

Answer

The peering connection failed because security groups in both VPCs block ICMP; update the security groups to allow all traffic and peering will succeed.

Answer

VPC peering requires a Transit Gateway when CIDR blocks match; attach both VPCs to a Transit Gateway to enable overlapping-range routing.

Answer

Enable DNS resolution over the peering connection so that private hostnames resolve, which will allow traffic to route despite the identical CIDR ranges.