Virtual Ethernet provides similar function as a 1 Gigabit (Gb) Ethernet adapter. A logical partition can use virtual Ethernet to establish multiple high-speed interpartition connections within a single managed system. AIX®, i5/OS®, and Linux® logical partitions, as well as Windows® environments integrated on iSeries®, can communicate with each other using TCP/IP over the virtual Ethernet communications ports.
You can create virtual Ethernet adapters on an i5/OS logical partition either by using a Hardware Management Console (HMC) or by using Virtual Partition Manager. When you create a virtual Ethernet adapter on an i5/OS logical partition, a communications device called CMNxx displays in the operating system, where xx indicates digits that uniquely identify the device within the operating system. You can then configure TCP/IP for that communications device in the operating system, just as if it were a physical Ethernet adapter. After TCP/IP is configured for the communications device, the virtual Ethernet adapter can communicate with other virtual Ethernet adapters with the same virtual LAN ID. To learn how to create a virtual Ethernet adapter using an HMC, see Configuring a virtual Ethernet adapter for i5/OS.
IBM® Systems and eServer™ hardware contain an interpartition virtual switch that automatically connects virtual Ethernet adapters with the same virtual LAN ID. No special hardware or software is required for virtual Ethernet adapters to communicate over the virtual LAN.
If a logical partition on the virtual LAN is also connected to a physical LAN, then you can configure the operating system of that logical partition so that the logical partitions on the virtual LAN can communicate over the physical LAN. This allows the logical partitions on a managed system to share a physical connection to an external network. If desired, you can configure connections between the virtual LAN and multiple physical LANs, or you can configure redundant connections between a virtual LAN and a physical LAN (to enhance the reliability of the connection). The logical partition having the physical Ethernet adapter does not have to be the serving partition for virtual SCSI.
The logical partitions on a virtual LAN communicate with each other as peers. If you shut down any of the logical partitions on the virtual LAN, the other logical partitions on the virtual LAN are still able to communicate with each other over the virtual LAN. If you shut down a logical partition that owns an external network connection, the other logical partitions on the virtual LAN are no longer able to use that external network connection, but the logical partitions can still communicate with each other. The only exception to this rule for i5/OS is the i5/OS logical partition on managed systems that are partitioned using the Virtual Partition Manager. If the i5/OS logical partition is shut down, then all of the other logical partitions on the managed system are also shut down.
You can connect Windows environments integrated on iSeries to a virtual LAN. To do this, you must first create a virtual Ethernet adapter on the i5/OS logical partition whose I/O resources are used by the integrated environment. You must then configure an Ethernet line description that associates a network server description (NWSD) with the CMNxx device for the virtual Ethernet adapter that you have just created. The virtual Ethernet adapter then belongs to the integrated environment and cannot be used by the i5/OS logical partition. If you want to connect the integrated environment and the i5/OS logical partition whose resources are used by the integrated environment to the same virtual LAN, then you must create two virtual Ethernet adapters on the i5/OS logical partition with the same virtual LAN ID.
In this figure, you can see three logical partitions on an IBM eServer i5 server. An Integrated xSeries® Server (IXS) with Windows installed uses the I/O resources on the i5/OS logical partition. The i5/OS logical partition has two virtual Ethernet adapters that are connected to the same virtual LAN. One virtual Ethernet adapter is used by the i5/OS logical partition itself, and the other virtual Ethernet adapter is used by the IXS. Each of the other logical partitions has a virtual Ethernet adapter that is connected to the same virtual LAN as the virtual Ethernet adapters on the i5/OS logical partition. The virtual Ethernet adapter on the Linux logical partition is bridged to a physical Ethernet adapter that belongs to the Linux logical partition. This allows the AIX and i5/OS logical partitions and the IXS to connect to an external, physical LAN through the virtual LAN.
Observe the following limitations when you create virtual LANs on your managed system.
Also, when you create virtual Ethernet adapters on your managed system using the Virtual Partition Manager, you might inadvertently exceed the number of virtual slots allowed on the managed system. If you exceed this limit, then the managed system requires you to IPL the managed system before it creates the virtual Ethernet adapters. During the IPL, the managed system enables all the available slots on the managed system so that you never need to IPL the managed system again due to insufficient virtual slots.
For more information on how to create Ethernet line descriptions and how you connect a virtual Ethernet network to an external LAN, refer to the i5/OS topic TCP/IP techniques to connect virtual Ethernet to external LANs. Additional information about virtual Ethernet, along with scenarios that demonstrate this communication solution, can be found in the IBM Redbook LPAR Configuration and Management Working with System i® Logical Partitions.
For more information about converting your pre-existing System i virtual Ethernet configuration, see Converting your pre-existing virtual Ethernet configuration.
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