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Catalyst 3550 Multilayer Switch Software Configuration Guide
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Chapter 30 Configuring EtherChannels
Configuring EtherChannels
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 ports.
For compatibility with Catalyst 1900 series switches, configure the PAgP learning method on the
Catalyst 3550 switches to learn source-MAC addresses on the physical port. The switch then sends
packets to the Catalyst 1900 switch using the same interface in the EtherChannel from which it learned
the source address.
Note
The Catalyst 3550 supports address learning only on aggregate ports even though the physical-port
keyword is 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 to the Catalyst 3550 switch is a physical learner, we recommend that you configure
the switch as a physical-port learner by using the pagp learn-method physical-port interface
configuration command and to set the load-distribution method based on the source MAC address by
using the port-channel load-balance src-mac global configuration command. Use the pagp
learn-method command only in this situation.
Beginning in privileged EXEC mode, follow these steps to configure your switch as a PAgP
physical-port learner and to adjust the priority so that the same port in the bundle is selected for sending
packets:
Command
Purpose
Step 1
configure terminal
Enter global configuration mode.
Step 2
interface interface-id
Enter interface configuration mode, and specify the interface for
transmission.
Step 3
pagp learn-method physical-port
Select the PAgP learning method.
By default, aggregation-port learning is selected, which means
the switch sends packets to the source by using any of the
interfaces in the EtherChannel. With aggregate-port learning, it
is not important on which physical port the packet arrives.
Select physical-port to connect with another switch that is a
physical learner. Make sure to configure the port-channel
load-balance global configuration command to src-mac as
described in the
“Configuring EtherChannel Load Balancing”
The learning method must be configured the same at both ends
of the link.
Step 4
pagp port-priority priority
Assign a priority so that the selected interface is chosen for
packet transmission.
For priority, the range is 0 to 255. The default is 128. The higher
the priority, the more likely that the interface will be used for
PAgP transmission.
Step 5
end
Return to privileged EXEC mode.