Specifications

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Chapter 28 Configuring EtherChannels
Understanding EtherChannels
Port-Channel Interfaces
When you create a Layer 2 EtherChannel, a port-channel logical interface is involved. You can create
the EtherChannel in these ways:
• Use the channel-group interface configuration command. This command automatically creates the
port-channel logical interface when the channel group gets its first physical interface. The
channel-group command binds the physical (10/100/1000 ports) and the logical ports together as
shown in Figure 28-2.
• Use the interface port-channel port-channel-number global configuration command to manually
create the port-channel logical interface. Then use the channel-group channel-group-number
interface configuration command to bind the logical interface to a physical port. The
channel-group-number can be the same as the port-channel-number, or you can use a new number.
If you use a new number, the channel-group command dynamically creates a new port channel.
Each EtherChannel has a port-channel logical interface numbered from 1 to 12. This port-channel
interface number corresponds to the one specified with the channel-group interface configuration
command.
Figure 28-2 Relationship of Physical Ports, Logical Port Channels, and Channel Groups
After you configure an EtherChannel, configuration changes applied to the port-channel interface apply
to all the physical interfaces assigned to the port-channel interface. Configuration changes applied to the
physical interface affect only the interface where you apply the configuration. To change the parameters
of all ports in an EtherChannel, apply configuration commands to the port-channel interface, for
example, spanning-tree commands or commands to configure a Layer 2 EtherChannel as a trunk.
Port Aggregation Protocol
The Port Aggregation Protocol (PAgP) is a Cisco-proprietary protocol that can be run only on Cisco
switches and on those switches licensed by vendors to support PAgP. PAgP facilitates the automatic
creation of EtherChannels by exchanging PAgP packets between Ethernet interfaces.
By using PAgP, the switch learns the identity of partners capable of supporting PAgP and the capabilities
of each interface. It then dynamically groups similarly configured interfaces into a single logical link
(channel or aggregate port). Similarly configured interfaces are grouped based on hardware,
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10/100/1000 ports
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Logical
port-channel
Channel-group
binding