Allied Telesis AT-S62 - Manual (Page 124)

Chapter 8: Port Trunking
Section I: Basic Operations 124
An aggregate trunk can consist of any number of ports on a switch, but
only a maximum of eight ports can be active at a time. If an aggregate
trunk contains more ports than can be active at one time, the extra ports
are placed in a stand-by mode. Ports in the standby mode do not pass
network traffic, but they do transmit and accept LACP data unit
(LACPDU) packets, which the switch uses to search for LACP-compliant
devices.
Only ports on a switch that are part of an aggregator transmit LACPDU
packets. If a switch port that is part of an aggregator does not receive
LACPDU packets from its corresponding port on the other device, it
assumes that the other port is not part of an LACP aggregator. Instead it
functions as a normal Ethernet port by forwarding network traffic.
However, it does continue to send LACPDU packets. If it begins to
receive LACPDU packets, it automatically transitions to an active or
standby mode as part of an aggregate trunk.
If a switch is to support more than one aggregate trunk, it may be
necessary to place each trunk in a separate aggregator, while in other
cases you may be able to create just one aggregator and let the switch
discern the individual aggregate trunks for you, automatically. The
determining factor is whether the trunks are going to the same or
different devices. If the trunks are going to the same device, you need to
create a different aggregator for each trunk. If they are going to different
devices, you can create just one aggregator and the switch can form the
aggregate trunks itself.
Here are a two examples. Figure 33 illustrates an AT-8524M switch with
two LACP trunks, each containing three links. Since both aggregate
trunks go to the same 802.3ad-compliant device, in this case another
Fast Ethernet switch, each trunk requires a separate aggregator.