Allied Telesis AT-S63 - Manual (Page 132)

Chapter 7: Static and LACP Port Trunks
132 Section I: Basic Features
ports. This parameter can be adjusted on each port and is a hexadecimal
value in a range of 1 to FFFF. The lower the number, the higher the
priority. Ports with the highest priorities are designated as the active ports
in an aggregate trunk.
For example, if both 802.3ad-compliant devices support up to eight active
ports and there are a total of ten ports in the trunk, the eight ports with the
lowest priority settings are designated as the active ports, and the others
are placed in standby mode. If an active link goes down on a active port,
the standby port with the highest priority is automatically activated to take
its place.
The default value of a port’s priority number is equal to its port number in
hexadecimal. For example, the default values for ports 2 and 11 are 0002
and 000B, respectively.
The selection of the active links in an aggregate trunk is dynamic. It
changes as links are added, removed, lost or reestablished. For example,
if an active port loses its link and is replaced by another port in the standby
mode, the reestablishment of the link on the originally active port causes it
to return to the active state by virtue of its having a higher priority, while
the port that replaced it is returned to the standby mode.
In the unusual event that you set this parameter to the same value for
some or all of the ports of an aggregate trunk, the selection of active ports
is based on port numbering. The lower the port number, the higher the
priority.
Two conditions must be met in order for a port that is a member of an
aggregate trunk to function in the standby mode. First, the number of ports
in the trunk must exceed the highest allowed number of active ports and,
second, the port must be receiving LACPDU packets from the other
device. A port functioning in the standby mode does not forward network
traffic, but it does continue to send LACPDU packets. If a port that is part
of an aggregator does not receive LACPDU packets, it functions as a
normal Ethernet port and forwards network packets along with LACPDU
packets.
Load Distribution Methods
The load distribution method determines the manner in which the switch
distributes the traffic across the active ports of an aggregate trunk. The
method is assigned to an aggregator and applies to all aggregate trunks
within it. If you want to assign different load distribution methods to
different aggregate trunks, you must create a separate aggregator for
each trunk. For further information, refer to “Load Distribution Methods” on
page 134.