You can associate it to and from instances as you require, and it's allocated to your account until you choose to release it.

For more information about Elastic IP addresses and how to use them, see Elastic IP Addresses. Amazon provides a DNS server that resolves Amazon-provided IPv4 DNS hostnames to IPv4 addresses.

For more information about NAT, see RFC 1631: The IP Network Address Translator (NAT).

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For more information about the standards and specifications of private IPv4 addresses, see RFC 1918.

We allocate private IPv4 addresses to instances using DHCP.

You can optionally assign an IPv6 CIDR block to your VPC and subnets, and assign IPv6 addresses from that block to instances in your subnet. For more information about IPv6, see IP Addressing in Your VPC in the A private IPv4 address is an IP address that's not reachable over the Internet.

You can use private IPv4 addresses for communication between instances in the same network (EC2-Classic or a VPC).

If your firewall doesn't automatically allow DNS query responses, then you need to allow traffic from the IP address of the Amazon DNS server.

To get the IP address of the Amazon DNS server, use the following command from within your instance: A public IP address is an IPv4 address that's reachable from the Internet.

You can use the internal DNS hostname for communication between instances in the same network, but we can't resolve the DNS hostname outside the network that the instance is in.

An instance launched in a VPC receives a primary private IP address from the IPv4 address range of the subnet. If you don't specify a primary private IP address when you launch the instance, we select an available IP address in the subnet's IPv4 range for you.

Unlike primary private IP addresses, secondary private IP addresses can be reassigned from one instance to another. For instances launched in EC2-Classic, we release the private IPv4 address when the instance is stopped or terminated.

If you restart your stopped instance, it receives a new private IPv4 address.

Each instance in a VPC has a default network interface (eth0) that is assigned the primary private IPv4 address.