When creating an account in AWS, you will find that a default VPC has been created within each AWS Region. A default VPC is a quick-start option that allows you to use AWS without having to create your own VPC and define your own subnets. A default VPC will have subnets already created. You can launch EC2 instances into your default VPCs in all regions and use other services such as Elastic Load Balancing, Auto Scaling, and Amazon RDS in any default VPC. While a default VPC can help you get off the ground rapidly when running tests, Proof of Concepts (PoC), and demos, you should always consider building your own VPC according to your own requirements when it comes to production. For each region, the default VPCs that were created initially have the following characteristics:

• A default VPC has a /16 IPv4 CIDR block (172.31.0.0/16) with up to 65,536 private IPv4 addresses
• A default VPC has a default security group and a default network ACL
• There are default subnets in each availability zone with a size of /20 and up to 4,096 addresses per subnet
• Routing is created that allows all subnets to talk to each other
• An internet gateway (IGW) is created and a route to the IGW is created for internet traffic
• All subnets are considered public and public IPs are assigned automatically to all instances