single link, thus achieving substantial bandwidth and redundancy benefits.
It is often advisable to use an EtherChannel for key trunks in your
campus design. Notice that EtherChannel affects STP, because ordinarily
one or more of the links would be disabled to prevent a loop.
Be aware of the following guidelines for EtherChannel:
1. All Ethernet interfaces on all modules must support EtherChannel.
2. You have a maximum of eight interfaces per EtherChannel.
3. The ports do not need to be contiguous or on the same module.
4. All ports in the EtherChannel must be set for the same speed and
5. Enable all interfaces in the EtherChannel.
6. An EtherChannel will not form if one of the ports is a Switched
Port Analyzer (SPAN) destination.
7. For Layer 3 EtherChannels, assign a Layer 3 address to the portchannel
logical interface, not the physical interfaces.
8. Assign all EtherChannel ports to the same VLAN or ensure they
are all set to the same trunk encapsulation and trunk mode.
9. The same allowed range of VLANs must be configured on all
ports in an EtherChannel.
10. Interfaces with different STP port path costs can form an
11. After an EtherChannel has been configured, a configuration made
to the physical interfaces affects the physical interfaces only.
Layer 4 port numbers— either source, destination, or both source and
Here is an example:
Router# configure terminal
Router(config)# interface range fastethernet 2/2 -8
Router(config-if)# channel-group 2 mode desirable