Assigning prefixes to Amazon EC2 network interfaces - Amazon Elastic Compute Cloud

Assigning prefixes to Amazon EC2 network interfaces

You can assign a private IPv4 or IPv6 CIDR range, either automatically or manually, to your network interfaces. By assigning prefixes, you scale and simplify the management of applications, including container and networking applications that require multiple IP addresses on an instance.

The following assignment options are available:

  • 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.

Assigning prefixes has the following benefits:

  • 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.

Basics for assigning prefixes

  • 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:

    • The IPv4 prefix that you can specify is /28.

    • The IPv6 prefix that you can specify is /80.

    • The prefix is in the subnet CIDR of the network interface, and does not overlap with other prefixes or IP addresses assigned to existing resources in the subnet.

  • 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:

    • us-east-1 Region

      ip-private-ipv4-address.ec2.internal
    • All other Regions

      ip-private-ipv4-address.region.compute.internal

Considerations and limits for prefixes

Take the following into consideration when you use prefixes:

  • Network interfaces with prefixes are supported with instances built on the Nitro System.

  • Prefixes for network interfaces are limited to private IPv4 addresses and IPv6 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 IP addresses per network interface per instance type.

  • Prefixes are included in source/destination checks.