Solution
EtherChannel can be configured manually with the appropriate commands, or it can be configured automatically if the switch negotiates the channel with the other side using Port Aggregation Protocol (PAgP). It is best to use the PAgP desirable mode to configure EtherChannel whenever possible. Sometimes when EtherChannel is configured manually, there are complications.
To create the channel manually, use the set port channel mod/port on command for each switch.
For step-by-step configuration instructions, refer to Configure EtherChannel Between Catalyst 4500/4000, 5500/5000, and 6500/6000 Switches That Run CatOS System Software.
After the channel configuration, it is important that all member ports of the ettherchannel should have a physical link to the other side of the etherchannel. If the other ports that do not have a physical connection, the the show port channel command output shows 'notconnect' and it would not help in effective sharing of traffic among the links in the channel.
For additional reference, refer to Sample Configuration: EtherChannel Between Catalyst Switches Running CatOS
