Shared Ethernet Adapters

With Shared Ethernet Adapters on the Virtual I/O Server logical partition, virtual Ethernet adapters on client logical partitions can send and receive outside network traffic.

A Shared Ethernet Adapter is a Virtual I/O Server component that bridges a physical Ethernet adapter and one or more virtual Ethernet adapters:

The real adapter can be a physical Ethernet adapter, a Link Aggregation or EtherChannel device, or a Logical Host Ethernet Adapter . The real adapter cannot be another Shared Ethernet Adapter or a VLAN pseudo-device.
The virtual Ethernet adapter must be a virtual I/O Ethernet adapter. It cannot be any other type of device or adapter.

Using a Shared Ethernet Adapter, logical partitions on the virtual network can share access to the physical network and communicate with stand-alone servers and logical partitions on other systems. The Shared Ethernet Adapter eliminates the need for each client logical partition to a dedicated physical adapter to connect to the external network.

A Shared Ethernet Adapter provides access by connecting the internal VLANs with the VLANs on the external switches. Using this connection, logical partitions can share the IP subnet with stand-alone systems and other external logical partitions. The Shared Ethernet Adapter forwards outbound packets received from a virtual Ethernet adapter to the external network and forwards inbound packets to the appropriate client logical partition over the virtual Ethernet link to that logical partition. The Shared Ethernet Adapter processes packets at layer 2, so the original MAC address and VLAN tags of the packet are visible to other systems on the physical network.

The Shared Ethernet Adapter has a bandwidth apportioning feature, also known as Virtual I/O Server quality of service (QoS). QoS allows the Virtual I/O Server to give a higher priority to some types of packets. In accordance with the IEEE 801.q specification, Virtual I/O Server administrators can instruct the Shared Ethernet Adapter to inspect bridged VLAN-tagged traffic for the VLAN priority field in the VLAN header. The 3-bit VLAN priority field allows each individual packet to be prioritized with a value from 0 to 7 to distinguish more important traffic from less important traffic. More important traffic is sent preferentially and uses more Virtual I/O Server bandwidth than less important traffic.

Note: To use this feature, when the Virtual I/O Server Trunk Virtual Ethernet Adapter is configured on an HMC, the adapter must be configured with additional VLAN IDs because only the traffic on these VLAN IDs is delivered to the Virtual I/O Server with a VLAN tag. Untagged traffic is always treated as though it belonged to the default priority class that is, as if it had a priority value of 0.

Depending on the VLAN priority values found in the VLAN headers, packets are prioritized as follows.

Table 1. VLAN traffic priority values and relative importance
Priority value and importance
1 (Most important) 2 0 (Default) 3 4 5 6 7 (Least important)

The Virtual I/O Server administrator can use QoS by setting the Shared Ethernet Adapter qos_mode attribute to either strict or loose mode. The default is disabled mode. The following definitions describe these modes:

disabled mode

This is the default mode. VLAN traffic is not inspected for the priority field. An example follows:

chdev -dev <SEA device name> -attr qos_mode=disabled

strict mode

More important traffic is bridged over less important traffic. This mode provides better performance and more bandwidth to more important traffic; however, it can result in substantial delays for less important traffic. An example follows:

chdev -dev <SEA device name> -attr qos_mode=strict

loose mode

A cap is placed on each priority level so that after a number of bytes is sent for each priority level, the following level is serviced. This method ensures that all packets are eventually sent. More important traffic is given less bandwidth with this mode than with strict mode; however, the caps in loose mode are such that more bytes are sent for the more important traffic, so it still gets more bandwidth than less important traffic. An example follows:

chdev -dev <SEA device name> -attr qos_mode=loose

Note: In either strict or loose mode, because the Shared Ethernet Adapter uses several threads to bridge traffic, it is still possible for less important traffic from one thread to be sent before more important traffic of another thread.

In SEA, QoS is provided per SEA thread. By default, SEA runs in thread mode with seven threads. When SEA receives traffic, it routes the traffic to a thread, based on source and destination information. If the QoS mode is enabled, it further queues the traffic, based on its priority, to the appropriate priority queue associated with the selected thread. Queued traffic for a particular thread is serviced in the order of higher to lower priority. All threads handle all priorities.

Note: SEA QoS does not assure bandwidth for a particular priority.

The effect of SEA QoS can be seen when there is enough traffic to keep all SEA threads busy, such that when a SEA thread is scheduled to run, it has enough higher priority traffic to service before it can get to the lower priority traffic. SEA QoS is not effective when the traffic pattern is such that the higher and lower priority traffic is spread across different threads.

GARP VLAN Registration Protocol

Shared Ethernet Adapters, in Virtual I/O Server version 1.4 or later, support GARP VLAN Registration Protocol (GVRP), which is based on Generic Attribute Registration Protocol (GARP). GVRP allows for the dynamic registration of VLANs over networks, which can reduce the number of errors in the configuration of a large network. By propagating registration across the network through the transmission of Bridge Protocol Data Units (BPDUs), devices on the network have accurate knowledge of the bridged VLANs configured on the network.

When GVRP is enabled, communication travels one way, from the Shared Ethernet Adapter to the switch. The Shared Ethernet Adapter notifies the switch which VLANs can communicate with the network. The Shared Ethernet Adapter does not configure VLANs to communicate with the network based on information received from the switch. Rather, the configuration of VLANs that communicate with the network is statically determined by the virtual Ethernet adapter configuration settings.

Host Ethernet Adapter or Integrated Virtual Ethernet

With Virtual I/O Server version 1.4, you can assign a logical host Ethernet port, of a logical host Ethernet adapter (LHEA), which is sometimes referred to as Integrated Virtual Ethernet, as the real adapter of a Shared Ethernet Adapter. The logical host Ethernet port is associated with a physical port on the Host Ethernet Adapter. The Shared Ethernet Adapter uses the standard device driver interfaces provided by the Virtual I/O Server to communicate with the Host Ethernet Adapter.

To use a Shared Ethernet Adapter with a Host Ethernet Adapter, the following requirements must be met:

The logical host Ethernet port must be the only port assigned to the physical port on the Host Ethernet Adapter. No other ports of the LHEA can be assigned to the physical port on the Host Ethernet Adapter.
The LHEA on the Virtual I/O Server logical partition must be set to promiscuous mode. (In an Integrated Virtualization Manager environment, the mode is set to promiscuous by default.) Promiscuous mode allows the LHEA (on the Virtual I/O Server) to receive all unicast, multicast, and broadcast network traffic from the physical network.

Recommendations

Consider using Shared Ethernet Adapters on the Virtual I/O Server in the following situations:

When the capacity or the bandwidth requirement of the individual logical partition is inconsistent or is less than the total bandwidth of a physical Ethernet adapter. Logical partitions that use the full bandwidth or capacity of a physical Ethernet adapter should use dedicated Ethernet adapters.
If you plan to migrate a client logical partition from one system to another.

Consider assigning a Shared Ethernet Adapter to a Logical Host Ethernet port when the number of Ethernet adapters that you need is more than the number of ports available on the LHEA, or you anticipate that your needs will grow beyond that number. If the number of Ethernet adapters that you need is fewer than or equal to the number of ports available on the LHEA, and you do not anticipate needing more ports in the future, you can use the ports of the LHEA for network connectivity rather than the Shared Ethernet Adapter.

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Last updated: Thu, June 12, 2014