Configuration for internet access

To enable your instances to receive or send traffic from the internet, do the following:

To provide your instances with internet access without assigning them public IP addresses, use a NAT device instead. A NAT device enables instances in a private subnet to connect to the internet, but prevents hosts on the internet from initiating connections with the instances. For more information, see NAT devices.

Public and private subnets

If a subnet is associated with a route table that has a route to an internet gateway, it's known as a public subnet. If a subnet is associated with a route table that does not have a route to an internet gateway, it's known as a private subnet.

In your public subnet's route table, you can specify a route for the internet gateway to all destinations not explicitly known to the route table (0.0.0.0/0 for IPv4 or ::/0 for IPv6). Alternatively, you can scope the route to a narrower range of IP addresses; for example, the public IPv4 addresses of your company’s public endpoints outside of Amazon, or the Elastic IP addresses of other Amazon EC2 instances outside your VPC.

IP addresses and NAT

To enable communication over the internet for IPv4, your instance must have a public IPv4 address. You can either configure your VPC to automatically assign public IPv4 addresses to your instances, or you can assign Elastic IP addresses to your instances. Your instance is only aware of the private (internal) IP address space defined within the VPC and subnet. The internet gateway logically provides the one-to-one NAT on behalf of your instance, so that when traffic leaves your VPC subnet and goes to the internet, the reply address field is set to the public IPv4 address or Elastic IP address of your instance, and not its private IP address. Conversely, traffic that's destined for the public IPv4 address or Elastic IP address of your instance has its destination address translated into the instance's private IPv4 address before the traffic is delivered to the VPC.

To enable communication over the internet for IPv6, your VPC and subnet must have an associated IPv6 CIDR block, and your instance must be assigned an IPv6 address from the range of the subnet. IPv6 addresses are globally unique, and therefore public by default.

In the following diagram, the subnet in Availability Zone A is a public subnet. The route table for this subnet has a route that sends all internet-bound IPv4 traffic to the internet gateway. The instances in the public subnet must have public IP addresses or Elastic IP addresses to enable communication with the internet over the internet gateway. For comparison, the subnet in Availability Zone B is a private subnet because its route table does not have a route to the internet gateway. Because there is no route to the internet gateway, instances in the private subnet can't communicate with the internet even if they have public IP addresses.

Internet access for default and nondefault VPCs

The following table provides an overview of whether your VPC automatically comes with the components required for internet access over IPv4 or IPv6.

For more information about default VPCs, see Default VPCs. For more information about creating a VPC, see Create a VPC.