HP 4800G Series Configuration Manual page 55

A port that joins the aggregation group after the limit on the number of selected ports has been reached
will not be placed in the selected state even if it should be in normal cases. This can prevent the ongoing
traffic on the current selected ports from being interrupted. You should avoid the situation however, as
this may cause the selected/unselected state of a port to change after a reboot.
Dynamic aggregation mode
LACP is enabled on member ports in a dynamic aggregation group.
In a dynamic aggregation group,
A selected port can receive and transmit LACPDUs.
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:
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.
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.
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.
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.
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