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Chapter 7: LACP Port Trunks
106
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 255, based on the port
number. For instance, the priority values for ports 2 and 11 are 002 and
011, respectively. 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 six active
ports and there are a total of eight ports in the trunk, the six 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 reestablished. 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.