Think of a scenario--you have already set up a VPC with instances inside it with, say, 172.0.x.x/16 CIDR and you've realized that the client who is going to connect also has the same CIDR block. So, wisely choose the IP address ranges for your VPC to avoid conflict with another network that you might connect to.
Troubleshooting IP address overlapping
Getting ready
You will need access to modify the VPC.
How to do it...
The only option is to create a new VPC and migrate resources into the new one. Please follow the steps given in Chapter 2, Building Your Own Custom...