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To add an additional network interface to an instance or to remove an interface from your instance perform the steps described below.

 The Please note: The steps below only provide a basic overview. The exact tasks required will vary depending on your network design. Please refer to the AWS documentation for details.

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When an instance is created, a default Ethernet interface is attached to the system. This is the primary network interface. You can create additional network interfaces and attach them to an instance. 

 Please note: If an instance has only one Ethernet interface, a public IP address can be assigned to the interface automatically. However, this automatically assigned address will be removed by AWS if a second interface is added to the instance and the instance is stopped and restarted. Be careful not to lose connectivity to your instance when changing the network configuration. Refer to the section about Elastic IP Addresses for additional information.

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Assigning an Elastic IP Address to the Network Interface

Please note:

• 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. Also this address will be removed after adding a second interface to the instance and restarting the instance.
• 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.

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• 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.

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• 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.

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1. Select your instance in the instance list and use the menu Actions > Networking > Detach Network Interface. Or,
2. Select your network interface in the network interface list and use the menu Actions > Detach.

 Take Take care that this step will not make your instance unreachable.

 The Please note: the primary network interface cannot be detached.

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• The first (primary) interface is called ensX (where X is an integer denoting the interface number; example: ens5).
• When a second interface is added to a running instance, it may initially be called eth0.
  However, the command ethtool -i eth0 shows that the enhanced network driver (ena) will be used for this interface. This interface will change its name to ensY (where Y is X+1) after restarting the instance. This means that any configuration file created for this interface must use the final name of the interface instead of eth0. Otherwise, the instance may become unreachable after a restart because there is no valid interface configuration (NetworkManager is not enabled on Charon-SSP AWS, so a configuration file must exist to configure the interface properly).
   This numbering scheme Please note: this numbering sequence may change in the future. Currently, it It is based on the PCI slot on which the Ethernet controller is presented and which is incremented by one for each additional Ethernet interface added. On the Charon host system, the slot can be verified with the following command:
  # lspci -vv | grep -A20 Ethernet

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• Manually assigning a private IP address from the subnet range.
• Enabling or disabling the automatic assignment of a private IP address to deviate from the subnet setting.
• Manually assigning a public IP address from the AWS range or the customer range.

Please note: Public IP addresses are not directly visible to the instance. The instance operating system always works with the private address. For external connections, the private address is mapped to the public IP address via NAT.

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• 10.1.1.0: the network address
• 10.1.1.1: reserved by AWS for the VPC router
• 10.1.1.2: reserved by AWS in any subnet; the second host address in the base VPC network range is the DNS server for the VPC.
• 10.1.1.3: reserved by AWS for future use
• 10.1.1.255: network broadcast address; AWS networks do not use broadcasts.

Please note: An automatically assigned public IP address is released (and not re-assigned) by AWS for example if

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See https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/using-instance-addressing.html for details.

Please note: An automatically assigned public IP address is not persistent. Every time a instance starts, it is assigned a new public IP address. If persistent public addresses are needed, use Elastic IP addresses.

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