Allied Telesis AT-GS950/24 - Manual (Page 112)

Chapter 7: LACP Port Trunks
112
Port Priority Value
The switch uses a port’s LACP priority to determine which ports are active
and which are in the standby mode in situations where the number of ports
in the aggregate trunk exceeds the highest allowed number of active
ports. This parameter is a value in a range of 1 to 65535, based on the
port number. 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 nine or more ports in the trunk, the eight ports
with the highest priorities (lowest priority values) are designated as the
active ports, and the others are placed in the standby mode. If an active
link goes down on a active port, the standby port with the next-highest
priority is automatically activated to take its place.
The selection of the active links in an aggregate trunk is dynamic and
changes as links are added, removed, lost, or re-established. For
example, if an active port loses its link and is replaced by another port in
the standby mode, the re-establishment of the link on the originally active
port causes the port to return to the active state by virtue of having a
higher priority value than the replacement port, which returns to the
standby mode.
Two conditions must be met for a port in 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. However, it continues 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.
Note
You can adjust the value of a port’s priority.