EtherChannel

EtherChannel allows you to bundle redundant links and treat them as a 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.

Following are guidelines for EtherChannel:

■ All Ethernet interfaces on all modules must support EtherChannel.

■ You have a maximum of eight interfaces per EtherChannel.

■ The ports do not need to be contiguous or on the same module.

■ All ports in the EtherChannel must be set for the same speed and duplex.

■ Enable all interfaces in the EtherChannel.

■ An EtherChannel will not form if one of the ports is a Switched Port Analyzer (SPAN) destination.

■ For Layer 3 EtherChannels, assign a Layer 3 address to the portchannel logical interface, not the physical interfaces.

■ Assign all EtherChannel ports to the same VLAN or ensure they are all set to the same trunk encapsulation and trunk mode.

■ The same allowed range of VLANs must be configured on all ports in an EtherChannel.

■ Interfaces with different STP port path costs can form anEtherChannel.

■ After an EtherChannel has been configured, a configuration made to the physical interfaces affects the physical interfaces only.

EtherChannel load balancing can use MAC addresses, IP addresses, or Layer 4 port numbers—either source, destination, or both source and destination addresses.

Here is an example:

Router# configure terminal
Router(config)# interface range fastethernet 2/2 -8
Router(config-if)# channel-group 2 mode desirable
Router(config-if)# end