aws - Default VPC and default subnets

Default VPC components

When we create a default VPC, we do the following to set it up for you:

• Create a VPC with a size /16 IPv4 CIDR block (172.31.0.0/16). This provides up to 65,536 private IPv4 addresses.

• Create a size /20 default subnet in each Availability Zone. This provides up to 4,096 addresses per subnet, a few of which are reserved for our use.

• Create an internet gateway and connect it to your default VPC.

• Add a route to the main route table that points all traffic (0.0.0.0/0) to the internet gateway.

• Create a default security group and associate it with your default VPC.

• Create a default network access control list (ACL) and associate it with your default VPC.

• Associate the default DHCP options set for your AWS account with your default VPC.

 

The following figure illustrates the key components that we set up for a default VPC.

 

 

 

 

 

Default subnets

By default, a default subnet is a public subnet, because the main route table sends the subnet's traffic that is destined for the internet to the internet gateway. You can make a default subnet into a private subnet by removing the route from the destination 0.0.0.0/0 to the internet gateway. However, if you do this, no EC2 instance running in that subnet can access the internet.