IEEE 802.3ad Link Aggregation configuration

IEEE 802.3ad is a standard way of doing link aggregation. Conceptually, it works the same as EtherChannel in that several Ethernet adapters are aggregated into a single virtual adapter, providing greater bandwidth and protection against failures.

For example, ent0 and ent1 can be aggregated into an IEEE 802.3ad Link Aggregation called ent3; interface ent3 would then be configured with an IP address. The system considers these aggregated adapters as one adapter. Therefore, IP is configured over them as over any Ethernet adapter.

IEEE 802.3ad requires support in the switch.

The advantages of using IEEE 802.3ad Link Aggregation instead of EtherChannel are that you can use switches that support the IEEE 802.3ad standard but do not support EtherChannel and it provides protection against adapter failures.

When an IEEE 802.3ad aggregation is configured, link aggregation control protocol data units (LACPDUs) are exchanged between the server machine (host system) and the adjacent switch. Only the active channel, which could be either the primary channel or the backup adapter, exchanges LACPDU with the adjacent switch.

To be able to aggregate adapters (meaning that the switch allows them to belong to the same aggregation) they must be of the same line speed (for example, all 100 Mbps, or all 1 Gbps) and they must all be full duplex. If you attempt to place adapters of different line speeds or different duplex modes, the creation of the aggregation on the AIX® system succeeds, but the switch might not aggregate the adapters together. If the switch does not successfully aggregate the adapters together, you might notice a decrease in network performance. For information on how to determine whether an aggregation on a switch was successful, see IEEE 802.3ad Link Aggregation troubleshooting.

According to the IEEE 802.3ad specification, packets that are being sent to the same IP address are sent over the same adapter. Thus, when being operated in 802.3ad mode, the packets are always distributed in the standard fashion, never in a round-robin fashion.

The backup adapter feature is available for IEEE 802.3ad Link Aggregations just as it is for EtherChannel. The backup adapter also follows the IEEE 802.3ad LACP. The switch port connected to the backup adapter must also have IEEE 802.3ad enabled.

For information in how to configure an IEEE 802.3ad aggregation, see Configuring IEEE 802.3ad Link Aggregation.

Consider the following before you configure an IEEE 802.3ad Link Aggregation:

• Although not officially supported, the AIX implementation of IEEE 802.3ad allows the Link Aggregation to contain adapters of different line speeds. However, you must aggregate only those adapters that are set to the same line speed and are set to full duplex. This helps to avoid potential problems in configuring the Link Aggregation on the switch. For more information on the types of aggregation allowed by your switch, see the documentation of your switch.
• If you are using 10/100 Ethernet adapters in the Link Aggregation, you must enable link polling on those adapters before you add them to the aggregation. Type smitty chgenet at the command line. Change the Enable Link Polling value to yes, and press Enter. Perform this action for every 10/100 Ethernet adapter that you are adding to your Link Aggregation.
  Note: In AIX 5L Version 5.2 with the 5200-03 Recommended Maintenance package and later, enabling the link polling mechanism is not necessary. The link poller is started automatically.