Allied Telesis AT-S62 - Manual (Page 128)

Chapter 8: Port Trunking
Section I: Basic Operations 128
LACP Port Priority Parameter
The switch uses this parameter to determine which ports are to be active
and which are to be in the standby mode in situations where the
number of ports in an aggregate trunk exceeds the highest allowed
number of active 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 original 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 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.