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35-3
Catalyst 3560 Switch Software Configuration Guide
OL-8553-06
Chapter 35 Configuring EtherChannels and Link-State Tracking
Understanding EtherChannels
If a link within an EtherChannel fails, traffic previously carried over that failed link moves to the
remaining links within the EtherChannel. If traps are enabled on the switch, a trap is sent for a failure
that identifies the switch, the EtherChannel, and the failed link. Inbound broadcast and multicast packets
on one link in an EtherChannel are blocked from returning on any other link of the EtherChannel.
Port-Channel Interfaces
When you create an EtherChannel, a port-channel logical interface is involved:
• With Layer 2 ports, use the channel-group interface configuration command to dynamically create
the port-channel logical interface.
You also can use the interface port-channel port-channel-number global configuration command
to manually create the port-channel logical interface, but then you must use the channel-group
channel-group-number 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.
• With Layer 3 ports, you should manually create the logical interface by using the interface
port-channel global configuration command followed by the no switchport interface configuration
command. Then you manually assign an interface to the EtherChannel by using the channel-group
interface configuration command.
For both Layer 2 and Layer 3 ports, the channel-group command binds the physical port and the logical
interface together as shown in
Figure 35-2.
Each EtherChannel has a port-channel logical interface numbered from 1 to 48. This port-channel
interface number corresponds to the one specified with the channel-group interface configuration
command.
Figure 35-2 Relationship of Physical Ports, Logical Port Channels, and Channel Groups
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Channel-group
binding
Physical ports
Logical
port-channel