Etherchannel and switch requirement

In AIX, you can configure multiple EtherChannels per system, but it is required that all the links in one EtherChannel are attached to a single switch. Because the EtherChannel cannot be spread across two switches, the entire EtherChannel is lost if the switch is unplugged or fails. To solve this problem, a new backup option available in AIX 5.2 and later keeps the service running when the main EtherChannel fails. The backup and EtherChannel adapters should be attached to different network switches, which must be inter-connected for this setup to work properly. In the event that all of the adapters in the EtherChannel fail, the backup adapter will be used to send and receive all traffic. When any link in the EtherChannel is restored, the service is moved back to the EtherChannel.

For example, ent0 and ent1 could be configured as the main EtherChannel adapters, and ent2 as the backup adapter, creating an EtherChannel called ent3. Ideally, ent0 and ent1 would be connected to the same EtherChannel-enabled switch, and ent2 would be connected to a different switch. In this example, all traffic sent over en3 (the EtherChannel's interface) would be sent over ent0 or ent1 by default (depending on the EtherChannel's packet distribution scheme), whereas ent2 will be idle. If at any time both ent0 and ent1 fail, all traffic would be sent over the backup adapter, ent2. When either ent0 or ent1 recover, they will once again be used for all traffic.

http://publib16.boulder.ibm.com/doc_link/en_US/a_doc_lib/aixbman/commadmn/tcp_etherchannel.htm

http://publib.boulder.ibm.com/infocenter/pseries/v5r3/index.jsp?topic=/com.ibm.aix.commadmn/doc/commadmndita/etherchannel_intro.htm