Cisco IE 4000, Software Configuration Manual

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1034
Configuring EtherChannels
Information About Configuring EtherChannels
With destination-IP address-based forwarding, when packets are forwarded to an EtherChannel, they are distributed
across the ports in the EtherChannel based on the destination-IP address of the incoming packet. Therefore, to provide
load-balancing, packets from the same IP source address sent to different IP destination addresses could be sent on
different ports in the channel. But packets sent from different source IP addresses to the same destination IP address
are always sent on the same port in the channel.
With source-and-destination IP address-based forwarding, packets are sent to an EtherChannel and distributed across
the EtherChannel ports, based on both the source and destination IP addresses of the incoming packet. This forwarding
method, a combination of source-IP and destination-IP address-based forwarding, can be used if it is not clear whether
source-IP or destination-IP address-based forwarding is better suited on a particular switch. In this method, packets
sent from the IP address A to IP address B, from IP address A to IP address C, and from IP address C to IP address B
could all use different ports in the channel.
Different load-balancing methods have different advantages, and the choice of a particular load-balancing method
should be based on the position of the switch in the network and the kind of traffic that needs to be load-distributed. In
Figure 110 on page 1035 , an EtherChannel from a switch that is aggregating data from four workstations communicates
with a router. Because the router is a single-MAC-address device, source-based forwarding on the switch EtherChannel
ensures that the switch uses all available bandwidth to the router. The router is configured for destination-based
forwarding because the large number of workstations ensures that the traffic is evenly distributed from the router
EtherChannel.
Use the option that provides the greatest variety in your configuration. For example, if the traffic on a channel is only
going to a single MAC address, using the destination-MAC address always chooses the same link in the channel. Using
source addresses or IP addresses might result in better load balancing.