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31-3
Cisco ME 3400 Ethernet Access Switch Software Configuration Guide
78-17058-01
Chapter 31 Configuring EtherChannels
Understanding EtherChannels
You can configure an EtherChannel in one of these modes: Port Aggregation Protocol (PAgP), Link
Aggregation Control Protocol (LACP), or On mode. PAgP and LACP are available only on NNIs.
Configure both ends of the EtherChannel in the same mode:
• When you configure one end of an EtherChannel in either PAgP or LACP mode, the system
negotiates with the other end of the channel to determine which ports should become active.
Incompatible ports are suspended.
• When you configure an EtherChannel in the on mode, no negotiations take place. The switch forces
all compatible ports to become active in the EtherChannel. The other end of the channel (on the other
switch) must also be configured in the on mode; otherwise, packet loss can occur.
If a link within an EtherChannel fails, traffic previously carried over that failed link changes to the
remaining links within the EtherChannel. A trap is sent for a failure, identifying 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 31-2.
Note The switch must be running the metro IP access image to support Layer 3 ports.
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.