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Cisco IE 3000 Switch Software Configuration Guide
OL-13018-03
Chapter 38 Configuring EtherChannels and Link-State Tracking
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 (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.
Note
The switch 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.
When the link partner of the IE 3000 switch is a physical learner (such as a Catalyst 1900 series switch),
we recommend that you configure the IE 3000 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.
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. This procedure is optional.
Command
Purpose
Step 1
configure terminal
Enter global configuration mode.
Step 2
interface
interface-id
Specify the port for transmission, and enter interface
configuration mode.
