You can define a virtual network using Amazon Virtual Private Cloud (Amazon VPC). You can select IP address ranges, create subnets, and configure route tables and network gateways. For example, for a three-tier web application, you can create a public subnet for the web servers and a private subnet for the application and database servers. Amazon VPC allows you to extend your corporate network into a private cloud contained within AWS. The IPSec tunnel mode enables you to create a secure connection between a gateway in your data center and a gateway in AWS cloud.