Prefix delegation for Amazon EC2 network interfaces

Automatic assignment — AWS chooses the prefix from your VPC subnet’s IPv4 or IPv6 CIDR block and assigns it to your network interface.

Manual Assignment — You specify the prefix from your VPC subnet’s IPv4 or IPv6 CIDR block, and AWS verifies that the prefix is not already assigned to other resources before assigning it to your network interface.

Increased IP addresses on a network interface — When you use a prefix, you assign a block of IP addresses as opposed to individual IP addresses. This increases the number of IP addresses for a network interface.

Simplified VPC management for containers — In container applications, each container requires a unique IP address. Assigning prefixes to your instance simplifies the management of your VPCs, as you can launch and terminate containers without having to call Amazon EC2 APIs for individual IP assignments.

You can assign a prefix to new or existing network interfaces.

To use prefixes, you assign a prefix to your network interface, attach the network interface to your instance, and then configure your operating system.

When you choose the option to specify a prefix, the prefix must meet the following requirements:

You can assign a prefix to the primary or secondary network interface.

You can assign an Elastic IP address to a network interface that has a prefix assigned to it.

You can also assign an Elastic IP address to the IP address part of the assigned prefix.

We resolve the private DNS host name of an instance to the primary private IPv4 address.

We assign each private IPv4 address for a network interface, including those from prefixes, using the following format:

Network interfaces with prefixes are supported with Nitro-based instances.

Prefixes for network interfaces are limited to IPv6 addresses and private IPv4 addresses.

The maximum number of IP addresses that you can assign to a network interface depends on the instance type. Each prefix that you assign to a network interface counts as one IP address. For example, a c5.large instance has a limit of 10 IPv4 addresses per network interface. Each network interface for this instance has a primary IPv4 address. If a network interface has no secondary IPv4 addresses, you can assign up to 9 prefixes to the network interface. For each additional IPv4 address that you assign to a network interface, you can assign one less prefix to the network interface. For more information, see Maximum IP addresses per network interface.

Prefixes are included in source/destination checks.

You must configure your operating system to work with network interfaces with prefixes. interfaces with prefixes. Note the following: