Cisco Systems 3750E manual Configuring the PAgP Learn Method and Priority, 37-19

Chapter 37 Configuring EtherChannels and Link-State Tracking

Configuring EtherChannels

	Command	Purpose
Step 3
	end	Return to privileged EXEC mode.
Step 4
	show etherchannel load-balance	Verify your entries.
Step 5
	copy running-config startup-config	(Optional) Save your entries in the configuration file.

To return EtherChannel load-balancing to the default configuration, use the no port-channelload-balanceglobal configuration command.

Configuring the PAgP Learn Method and Priority

Network devices are classified as PAgP physical learners or aggregate-port learners. A device is a physical learner if it learns addresses by physical ports and directs transmissions based on that knowledge. A device is an aggregate-port learner if it learns addresses by aggregate (logical) ports. The learn method must be configured the same at both ends of the link.

When a device and its partner are both aggregate-port learners, they learn the address on the logical port-channel. The device sends packets to the source by using any of the ports in the EtherChannel. With aggregate-port learning, it is not important on which physical port the packet arrives.

PAgP cannot automatically detect when the partner device is a physical learner and when the local device is an aggregate-port learner. Therefore, you must manually set the learning method on the local device to learn addresses by physical ports. You also must set the load-distribution method to source-based distribution, so that any given source MAC address is always sent on the same physical port.

You also can configure a single port within the group for all transmissions and use other ports for hot standby. The unused ports in the group can be swapped into operation in just a few seconds if the selected single port loses hardware-signal detection. You can configure which port is always selected for packet transmission by changing its priority with the pagp port-priorityinterface configuration command. The higher the priority, the more likely that the port will be selected.

Note The switch supports address learning only on aggregate ports even though the physical-portkeyword is provided in the CLI. The pagp learn-methodcommand and the pagp port-prioritycommand have no effect on the switch hardware, but they are required for PAgP interoperability with devices that only support address learning by physical ports, such as the Catalyst 1900 switch.

When the link partner of the Catalyst 3750-E or 3560-E switch is a physical learner (such as a Catalyst 1900 series switch), we recommend that you configure the Catalyst 3750-E or 3560-E switch as a physical-port learner by using the pagp learn-methodphysical-portinterface configuration command. Set the load-distribution method based on the source MAC address by using the port-channelload-balancesrc-macglobal configuration command. The switch then sends packets to the Catalyst 1900 switch using the same port in the EtherChannel from which it learned the source address. Only use the pagp learn-methodcommand in this situation.

	Catalyst 3750-E and 3560-E Switch Software Configuration Guide
OL-9775-02		37-19