Cisco 4500M Software Manual page 254

Overview of EtherChannel
The protocol learns the capabilities of LAN port groups dynamically and informs the other LAN ports.
Once LACP identifies correctly matched Ethernet links, it facilitates grouping the links into an
EtherChannel. The EtherChannel is then added to the spanning tree as a single bridge port.
Both the passive and active modes allow LACP to negotiate between LAN ports to determine if they can
form an EtherChannel, based on criteria such as port speed and trunking state. Layer 2 EtherChannels
also use VLAN numbers.
LAN ports can form an EtherChannel when they are in different LACP modes as long as the modes are
compatible. For example:
A LAN port in active mode can form an EtherChannel successfully with another LAN port that is
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in active mode.
A LAN port in active mode can form an EtherChannel with another LAN port in passive mode.
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A LAN port in passive mode cannot form an EtherChannel with another LAN port that is also in
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passive mode, because neither port will initiate negotiation.
LACP uses the following parameters:
LACP system priority—You may configure an LACP system priority on each switch running LACP.
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The system priority can be configured automatically or through the CLI. See the
LACP System Priority and System ID" section on page
the switch MAC address to form the system ID and also during negotiation with other systems.
Note
LACP port priority—You must configure an LACP port priority on each port configured to use
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LACP. The port priority can be configured automatically or through the CLI. See the
Layer 2 EtherChannels" section on page
form the port identifier.
Note Standby and "sub-channeling" are not supported in LACP and PagP.
LACP administrative key—LACP automatically configures an administrative key value equal to the
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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:
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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 can not be actively included in a channel, it
will not be included automatically if a channelled port fails.
Software Configuration Guide—Release 12.2(25)EW
17-4
The LACP system ID is the combination of the LACP system priority value and the MAC
address of the switch.
Port physical characteristics, such as data rate, duplex capability, and point-to-point or shared
medium
Configuration restrictions that you establish
Chapter 17 Understanding and Configuring EtherChannel
17-11. LACP uses the system priority with
17-9. LACP uses the port priority with the port number to
"Configuring the
"Configuring
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