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StepDetails
Locate the Network Interfaces option on the EC2 dashboard and click on it.

Clicking on Network Interfaces opens the list of existing networks.

Create a new interface.

Click on Create Network Interface at the top of the interface list.

This opens the interface creation window.

On this screen,

  • enter a description,
  • select the subnet the interface should be on (select the subnet to which your instance is to be connected),
  • allow AWS to automatically assign a private IP address or set a custom one from the subnet IP range, and
  • associate the interface with a security group (often the same as for the instance).

Click on Create when you are done. The new interface will appear in the overview list. There you can assign a name to the interface. Check that the interface is in state available.

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Warning
  • Stopping and restarting the instance after adding a second network interface will release any automatically assigned public IP address. If several interfaces and are required where one or more are configured with a public address are required, use Elastic IP addresses.
  • Additionally, adding a second network interface to a non-Amazon Linux EC2 instance causes traffic flow issues. This occurs in cases of asymmetric routing where traffic to the instance arrives at one network interface and leaves the instance through the other network interface. This is blocked by AWS because a mismatch between MAC address and IP address. Refer to the AWS documentation and AWS Networking and Charon-SSP for more information. Failure to use the proper steps, may make your instance unreachable!

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Assigning an Elastic IP Address to the Network Interface

The public IP address assigned to your instance by default when it starts, is not persistent. You will receive a new address when the instance is stopped and started again.

An Elastic IP address is a persistent, public IPv4 address to be used for one of your network interfaces or instances. You can associate an Elastic IP address with any instance or network interface in your account.

(info) The  The advantage of associating the Elastic IP address with the network interface instead of directly with the instance is that you can move the network interface with its attributes easily from one instance to another.

(warning) The  The initial automatically assigned public IP address will be removed as soon as you restart the instance after adding a network interface with an Elastic IP address to your instance. Do not restart your instance before you are sure you can reach it via the Elastic IP address. The automatically assigned public IP address will also be disabled if you assign an Elastic IP address to the primary Ethernet interface of the instance.

The table below describes the steps required to add an Elastic IP address to a network interface.

StepDetails
Locate the Elastic IPs option on the EC2 dashboard and click on it.

This will list the already created Elastic IP addresses.

Allocate a new address.

In the overview list, click on Allocate new address if you need to allocate a new address. It is also possible to assign an existing address to an interface. However, each address can only be used for one instance.

This will open the address allocation window.


In the address allocation window, select the Amazon pool (or your own pool of public addresses), and click on Allocate.

The new address will be shown in the list.

Associate the address with the network interface.

Right-click on the address and select Associate. A window to enter the required options opens.

In the window,

  • select to associate the IP address with a network interface,
  • select your network interface from the drop-down menu,
  • connect the public address to the private address of the interface, and 
  • click on Associate to complete the step.

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