Versions Compared

Old Version 35

changes.mady.by.user W.Erber

Saved on

compared with

New Version 36

changes.mady.by.user W.Erber

Saved on

Key

  • This line was added.
  • This line was removed.
  • Formatting was changed.
Comment: add interface naming section

...

Warning
  • 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 AWS Networking and the Charon-SSP 4.1.x for Marketplace - Configuration and Management Guide (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 names naming section in AWS Networking and Charon-SSPbelow and the AWS documenation.
  • 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.

...

(info) The primary network interface cannot be detached.

Interface Naming on Linux Hosts with Enhanced Networking

When looking at the instance from the AWS management console, the interface names are eth0, eth1, etc.

On instances without support for enhanced networking the Linux interface names are also eth0, eth1, etc.

However, on instances with support for enhanced networking, the names on the AWS level differ from those on the Linux level:

  • 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 maybe initially 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).
    (warning) This numbering scheme may change in the future. Currently, 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

(info) To avoid confusion before the instance can be restarted, the new interface can be renamed to its final name using the command 
     ip link set eth0 name ensY && ip link set ensY up


Include Page
KBCOMMON:DOC-GoToToc
KBCOMMON:DOC-GoToToc