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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.
Creating a New Network Interface
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- Stopping and restarting the instance after adding a second network interface will release any automatically assigned public IP address. If several interfaces are required where one or more are configured with a public address, use Elastic IP addresses.
- Additionally, adding a second IP 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 the Charon-SSP 4.1.x for Marketplace - Configuration and Management Guide /wiki/spaces/DocCHSSP420CLD/overview (section asymmetric routing considerations) for more information. Failure to use the proper steps, may make your instance unreachable!
- If your instance supports enhanced networking there may be naming inconsistencies when adding additional interfaces to a running instance. Please refer to the interface naming section below and the AWS documentation.
- The NetworkManager is disabled on Charon-SSP AWS. Therefore, ifcfg-files in /etc/sysconfig/network-scripts are required to define the IP configuration of an interface.
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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. 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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