Standard or 802.3ad algorithm

There are advantages to using the EtherChannel standard algorithm.

The standard algorithm is used for both standard and IEEE 802.3ad-style link aggregations. AIX® divides the last byte of the "numerical value" by the number of adapters in the EtherChannel and uses the remainder to identify the outgoing link. If the remainder is zero, the first adapter in the EtherChannel is selected; a remainder of one means the second adapter is selected, and so on (the adapters are selected in the order that they are listed in the adapter_names attribute).

The Hash Mode selection determines the numerical value used in the calculation. By default, the last byte of the destination IP address or MAC address is used in the calculation, but the source and destination TCP or UDP port values can also be used. These alternatives allow you to fine-tune the distribution of outgoing traffic across the real adapters in the EtherChannel.

In default hash mode, the adapter selection algorithm is applied to the last byte of the destination IP address for IP traffic. For ARP and other non-IP traffic, the same formula is applied on the last byte of the destination MAC address. Unless there is an adapter failure that causes a failover, all traffic between a host pair in default standard mode goes out over the same adapter. The default hash mode may be ideal when the local host establishes connections to many different IP addresses.

If the local host establishes lengthy connections to few IP addresses, however, you will notice that some adapters carry a greater load than others, because all of the traffic sent to a specific destination is sent over the same adapter. While this prevents packets from arriving out-of-order, it may not use bandwidth in the most effective fashion in all cases. The port-based hash modes still send packets in order, but they allow packets belonging to different UDP or TCP connections, even if they are sent to the same destination, to be sent over different adapters, thus better using the bandwidth of all of the adapters.

In src_dst_port hash mode, the TCP or UDP source and destination port values of the outgoing packet are added, then divided by two. The resultant whole number (no decimals) is plugged into the standard algorithm. TCP or UDP traffic is sent on the adapter selected by the standard algorithm and selected hash mode value. Non-TCP or UDP traffic will fall back to the default hash mode, meaning the last byte of either the destination IP address or MAC address. The src_dst_port hash mode option considers both the source and the destination TCP or UDP port values. In this mode, all of the packets in one TCP or UDP connection are sent over a single adapter so they are guaranteed to arrive in order, but the traffic is still spread out because connections (even to the same host) may be sent over different adapters. The results of this hash mode are not skewed by the connection establishment direction because it uses both the source and destination TCP or UDP port values.

In src_port hash mode, the source TCP or UDP port value of the outgoing packet is used. In dst_port hash mode, the destination TCP or UDP port value of the outgoing packet is used. Use the src_port or dst_port hash mode options if port values change from one connection to another and if the src_dst_port option is not yielding a desirable distribution.