Configuring The Pagp Learn Method And Priority - Cisco Catalyst 3750-X Software Configuration Manual

Chapter 40 Configuring EtherChannels and Link-State Tracking
Command
Step 3
end
Step 4
show etherchannel load-balance
Step 5 copy running-config startup-config
To return EtherChannel load-balancing to the default configuration, use the no port-channel
load-balance global 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-priority interface configuration command. The
higher the priority, the more likely that the port will be selected.
The switch supports address learning only on aggregate ports even though the physical-port keyword is
Note
provided in the CLI. The pagp learn-method command and the pagp port-priority command 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-X or 3560-X switch is a physical learner (such as a
Catalyst 1900 series switch), we recommend that you configure the Catalyst 3750-X or 3560-X switch
as a physical-port learner by using the pagp learn-method physical-port interface configuration
command. Set the load-distribution method based on the source MAC address by using the port-channel
load-balance src-mac global 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-method command in this situation.
OL-21521-01
Purpose
Return to privileged EXEC mode.
Verify your entries.
(Optional) Save your entries in the configuration file.
Catalyst 3750-X and 3560-X Switch Software Configuration Guide
Configuring EtherChannels
40-19