Load Balancing - Cisco Catalyst 4500 Series Configuration Manual

Chapter 24 Configuring EtherChannel and Link State Tracking
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LACP tries to configure the maximum number of compatible ports in an EtherChannel up to the
maximum allowed by the hardware (eight ports). If a port cannot be actively included in a channel, it is
not included automatically if a channelled port fails.
Note

Load Balancing

EtherChannel can balance the traffic load across the links in the channel 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) 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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OL-25340-01
LACP administrative key—LACP automatically configures an administrative key value equal to the
channel group identification number on each port configured to use LACP. The administrative key
defines the ability of a port to aggregate with other ports. A port's ability to aggregate with other
ports is determined by these factors:
– Port physical characteristics, such as data rate, duplex capability, and point-to-point or shared
medium
Configuration restrictions that you establish
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Standby and "sub-channeling" are not supported in LACP and PAgP.
24-14.
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. Disabling an interface in an EtherChannel is treated as a
link failure, and its traffic is transferred to one of the remaining interfaces in the EtherChannel.
An EtherChannel does 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
the channel.
EtherChannel Configuration Guidelines and Restrictions
"Configuring EtherChannel Load Balancing"
Software Configuration Guide—Release IOS XE 3.3.0SG and IOS 15.1(1)SG
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