Cisco Catalyst 2960 Software Configuration Manual page 879

Chapter 38 Configuring EtherChannels and Link-State Tracking
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.
When the link partner of the switch is a physical learner (such as a Catalyst 1900 series switch), we
recommend that you configure the Catalyst 2960, 2960-S, or 2960-C 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
Step 1 configure terminal
Step 2 interface interface-id
Step 3 pagp learn-method physical-port
OL-26520-01
Purpose
Enter global configuration mode.
Specify the port for transmission, and enter interface
configuration mode.
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 ports
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
section on page
The learning method must be configured the same at both ends
of the link.
Catalyst 2960 and 2960-S Switches Software Configuration Guide, Release 15.0(1)SE
Configuring EtherChannels
"Configuring EtherChannel Load Balancing"
38-16.
38-17