Understanding Load Balancing; Etherchannel Configuration Guidelines And Restrictions - Cisco 4500M Software Manual

Chapter 17 Understanding and Configuring EtherChannel

Understanding Load Balancing

EtherChannel can balance the traffic load across the links in the channel. It does this by reducing part of
the binary pattern formed from the addresses or ports in the frame to a numerical value that selects one
of the links in the channel. To balance the load, EtherChannel uses MAC addresses, IP addresses, or
Layer 4 port numbers, and either the message source or message destination, or both.
Use the option that provides the greatest variety in your configuration. For example, if the traffic on a
channel is going only 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.
Load balancing can only be configured globally. As a result, all channels (manually configured, PagP,
Note
or LACP) will use the same load balancing method.
For additional information on load balancing, see the
section on page

EtherChannel Configuration Guidelines and Restrictions

If improperly configured, some EtherChannel interfaces are disabled automatically to avoid network
loops and other problems. Follow these guidelines and restrictions to avoid configuration problems:
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All Ethernet interfaces on all modules support EtherChannel (maximum of eight interfaces) with no
requirement that interfaces be physically contiguous or on the same module.
Configure all interfaces in an EtherChannel to operate at the same speed and duplex mode.
Enable all interfaces in an EtherChannel. If you shut down an interface in an EtherChannel, it is
treated as a link failure and its traffic is transferred to one of the remaining interfaces in the
EtherChannel.
An EtherChannel will not form if one of the interfaces is a Switched Port Analyzer (SPAN)
destination port.
For Layer 3 EtherChannels:
Assign Layer 3 addresses to the port-channel logical interface, not to the physical interfaces in
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the channel.
For Layer 2 EtherChannels:
Assign all interfaces in the EtherChannel to the same VLAN, or configure them as trunks.
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If you configure an EtherChannel from trunk interfaces, verify that the trunking mode is the
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same on all the trunks. Interfaces in an EtherChannel with different trunk modes can have
unexpected results.
An EtherChannel supports the same allowed range of VLANs on all the interfaces in a trunking
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Layer 2 EtherChannel. If the allowed range of VLANs is not the same, the interfaces do not
form an EtherChannel.
Interfaces with different Spanning Tree Protocol (STP) port path costs can form an
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EtherChannel as long they are otherwise compatibly configured. Setting different STP port path
costs does not, by itself, make interfaces incompatible for the formation of an EtherChannel.
EtherChannel Configuration Guidelines and Restrictions
"Configuring EtherChannel Load Balancing"
Software Configuration Guide—Release 12.2(25)EW
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