Etherchannel notes

If you initially issue the channel-group command under the physical interface, it automatically creates the port-channel interface. If you configured the port-channel interface before you channeled physical interfaces, remove the port-channel interface first. This is only relevant on Catalyst switches. The order of configuration changes on the 7500 router. You must configure the port-channel interface before you configure the channel group under the physical interface.

The order of configuration of a port channel in Catalyst 6500/6000 and 4500/4000 Cisco IOS Software is important. It is best to issue any switchport command before you issue the channel-group command in a physical interface.

When you issue the channel-group command prior to the switchport command on a physical interface (interface Gigabit Ethernet 1/1), the port-channel interface is created automatically and becomes a L3 interface. If you then issue the switchport command under the physical interface, the physical interface becomes a L2 interface. Also, the port-channel interface that you created earlier has no physical interface associated with it. Notice that the channel-group command is absent from under the physical interface. In this case, you must first issue the switchport command under the newly configured port-channel interface. Then, the physical port accepts the channel-group command again. In this case, the port channel has changed from a L3 interface to a L2 interface.

Consider, in contrast, if you issue the switchport command first on a physical interface and then add the channel-group command. In this case, the port-channel interface is automatically created and inherits all the configured switchport commands.

On a Catalyst 6500/6000 switch running Cisco IOS Software, all ports are L3 ports by default. On a Catalyst 4500/4000 switch running Cisco IOS Software, all ports are L2 ports by default.