Amazon RDS lets you use the Amazon Virtual Private Cloud (VPC) service to create a virtual private cloud where you can launch a DB instance. When you use a virtual private cloud, you have control over your virtual networking environment: you can select your own IP address range, create subnets, and configure routing and access control lists. The basic functionality of Amazon RDS is the same whether it is running in a VPC or not: Amazon RDS manages backups, software patching, automatic failure detection, and recovery. There is no additional cost to run your DB instance in a VPC.
Amazon RDS supports two VPC platforms in each region: The EC2-Classic platform (shown as EC2,VPC in the RDS console) requires you to use the Amazon VPC service if you want to create a VPC, and the EC2-VPC platform (shown as VPC in the RDS console), which provides your AWS account with a default VPC in a region. If you are a new customer to Amazon RDS or if you are creating DB instances in a region you have not worked in before, chances are good you are on the EC2-VPC platform and that you have a default VPC. To determine which platform your account supports in a particular region, see Determining Whether You are Using the EC2-VPC or EC2-Classic Platform.
For more information about using a VPC with Amazon RDS, see Using Amazon RDS with Amazon Virtual Private Cloud (VPC)