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34-20
Cisco ME 3400 Ethernet Access Switch Software Configuration Guide
OL-9639-06
Chapter 34 Configuring EtherChannels and Link-State Tracking
Configuring EtherChannels
If you configure more than eight links for an EtherChannel group, the software automatically decides
which of the hot-standby ports to make active based on the LACP priority. The software assigns to every
link between systems that operate LACP a unique priority made up of these elements (in priority order):
• LACP system priority
• System ID (a combination of the LACP system priority and the switch MAC address)
• LACP port priority
• Port number
In priority comparisons, numerically lower values have higher priority. The priority decides which ports
should be put in standby mode when there is a hardware limitation that prevents all compatible ports
from aggregating.
Ports are considered for active use in aggregation in link-priority order starting with the port attached to
the highest priority link. Each port is selected for active use if the preceding higher priority selections
can also be maintained. Otherwise, the port is selected for standby mode.
You can change the default values of the LACP system priority and the LACP port priority to affect how
the software selects active and standby links. For more information, see the
“Configuring the LACP
System Priority” section on page 34-20 and the “Configuring the LACP Port Priority” section on
page 34-21.
Configuring the LACP System Priority
You can configure the system priority for all of the EtherChannels that are enabled for LACP by using
the lacp system-priority global configuration command. You cannot configure a system priority for
each LACP-configured channel. By changing this value from the default, you can affect how the software
selects active and standby links.
You can use the show etherchannel summary privileged EXEC command to see which ports are in the
hot-standby mode (denoted with an H port-state flag).
Beginning in privileged EXEC mode, follow these steps to configure the LACP system priority. This
procedure is optional.
To return the LACP system priority to the default value, use the no lacp system-priority global
configuration command.
Command Purpose
Step 1
configure terminal Enter global configuration mode.
Step 2
lacp system-priority priority Configure the LACP system priority.
For priority, the range is 1 to 65535. The default is 32768.
The lower the value, the higher the system priority.
Step 3
end Return to privileged EXEC mode.
Step 4
show running-config
or
show lacp sys-id
Verify your entries.
Step 5
copy running-config startup-config (Optional) Save your entries in the configuration file.