3Com 4210G Series, Configuration Manual, Page: 56 / 1133

2-5
Dynamic aggregation mode
LACP is enabled on member ports in a dynamic aggregation group.
In a dynamic aggregation group,
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A selected port can receive and transmit LACPDUs.
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An unselected port can receive and send LACPDUs only if it is up and with the same
configurations as those on the aggregate interface.
In a dynamic aggregation group, the system sets the ports to selected or unselected state in the
following steps:
1) The local system (the actor) negotiates with the remote system (the partner) to determine port
state based on the port IDs on the end with the preferred system ID. The following is the detailed
negotiation procedure:
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Compare the system ID (comprising the system LACP priority and the system MAC address) of
the actor with that of the partner. The system with the lower LACP priority wins out. If they are the
same, compare the system MAC addresses. The system with the smaller MAC address wins out.
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Compare the port IDs of the ports on the system with the smaller system ID. A port ID comprises a
port LACP priority and a port number. First compare the port LACP priorities. The port with the
lower LACP priority wins out. If two ports are with the same LACP priority, compare their port
numbers. The port with the smaller port ID, that is, the port with smaller port number, is selected
as the reference port.
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If a port (in up state) is with the same port attributes and class-two configuration as the reference
port, and the peer port of the port is with the same port attributes and class-two configurations as
the peer port of the reference port, consider the port as a candidate selected port; otherwise set
the port to the unselected state.
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The number of selected ports that an aggregation group can contain is limited. When the number
of candidate selected ports is under the limit, all the candidate selected ports are set to selected
state. When the limit is exceeded, the system selects the candidate selected ports with smaller
port IDs as the selected ports, and set other candidate selected ports to unselected state. At the
same time, the peer device, being aware of the changes, changes the state of its ports
accordingly.
2) Set the ports that cannot aggregate with the reference port to the unselected state.
For static and dynamic aggregation modes:
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In an aggregation group, the port to be a selected port must be the same as the reference port in
port attributes, and class-two configurations. To keep these configurations consistent, you should
configure the port manually.
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Because changing a port attribute or class-two configuration setting of a port may cause the select
state of the port and other member ports to change and thus affects services, you are
recommended to do that with caution.