Cisco Systems 3750E manual Configuring the Lacp System Priority, 37-21

Chapter 37 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. To every link between systems that operate LACP, the software assigns a unique priority made up of these elements (in priority order):

•LACP system priority

•System ID (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.

Determining which ports are active and which are hot standby is a two-step procedure. First the system with a numerically lower system priority and system-id is placed in charge of the decision. Next, that system decides which ports are active and which are hot standby, based on its values for port priority and port number. The port-priority and port-number values for the other system are not used.

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 37-21and the “Configuring the LACP Port Priority” section on page 37-22.

Configuring the LACP System Priority

You can configure the system priority for all the EtherChannels that are enabled for LACP by using the lacp system-priorityglobal 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.

	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	Verify your entries.
	or
	show lacp sys-id
Step 5
	copy running-config startup-config	(Optional) Save your entries in the configuration file.

To return the LACP system priority to the default value, use the no lacp system-priorityglobal configuration command.

	Catalyst 3750-E and 3560-E Switch Software Configuration Guide
OL-9775-02		37-21