Elastic network interfaces

Each instance has a default network interface, called the primary network interface. You can't detach a primary network interface from an instance.

You can create and attach secondary network interfaces to your instance. The maximum number of network interfaces varies by instance type. For more information, see Maximum IP addresses per network interface.

When you launch an EC2 instance into an IPv4-only or dual stack subnet, the instance receives a primary private IP address from the IPv4 address range of the subnet. You can also specify additional private IPv4 addresses, known as secondary private IPv4 addresses. Unlike primary private IP addresses, secondary private IP addresses can be reassigned from one instance to another.

All subnets have a modifiable attribute that determines whether network interfaces created in that subnet (and therefore instances launched into that subnet) are assigned a public IPv4 address. For more information, see Subnet settings in the Amazon VPC User Guide. When you launch an instance, the IP address is assigned to the primary network interface. If you specify an existing network interface as the primary network interface when you launch an instance, the public IPv4 address is determined by this network interface.

When you create a network interface, it inherits the public IPv4 addressing attribute from the subnet. If you later modify the public IPv4 addressing attribute of the subnet, the network interface keeps the setting that was in effect when it was created.

If you associate IPv6 CIDR blocks with your VPC and subnet, you can assign IPv6 addresses from the subnet range to a network interface. Each IPv6 address can be assigned to one network interface.

All subnets have a modifiable attribute that determines whether network interfaces created in that subnet (and therefore instances launched into that subnet) are automatically assigned an IPv6 address from the range of the subnet. When you launch an instance, the IPv6 address is assigned to the primary network interface.

You can associate an Elastic IP address with one of the private IPv4 addresses for the network interface. You can associate one Elastic IP address with each private IPv4 address. If you disassociate an Elastic IP address from a network interface, you can release it or associate it with a different instance.

You can set the termination behavior for a network interface that's attached to an instance. You can specify whether the network interface should be automatically deleted when you terminate the instance to which it's attached.

You can enable or disable source/destination checks, which ensure that the instance is either the source or the destination of any traffic that it receives. Source/destination checks are enabled by default. You must disable source/destination checks if the instance runs services such as network address translation, routing, or firewalls.

These network interfaces are created and managed by AWS services to enable you to use some resources and services. You can't manage these network interfaces yourself. For more information, see Requester-managed network interfaces.

A prefix is a reserved private IPv4 or IPv6 CIDR range that you allocate for automatic or manual assignment to network interfaces that are associated with an instance. By using Delegated Prefixes, you can launch services faster by assigning a range of IP addresses as a single prefix.