HP 1920 Series User Manual page 220

4.
5.
After a static aggregation group has reached the limit on Selected ports, any port that joins the group is
placed in the Unselected state to avoid traffic interruption on the existing Selected ports. However, the
state of link aggregation member ports might 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 send LACPDUs. An Unselected port
can receive and send LACPDUs only when it is up, and has the same configurations as the aggregate
interface.
In a dynamic aggregation group, the local system (the actor) negotiates with the remote system (the
partner) to determine the aggregation state of each port in the following steps:
1.
2.
3.
The number of Selected ports in an aggregation group is limited. When the number of Selected ports is
under the limit, all the member ports are set to Selected state. When the limit is exceeded, the system sets
the ports with smaller port IDs as the Selected ports, and place other ports in the Unselected state. At the
same time, the peer device, being aware of the changes, sets the aggregation state of local member
ports the same as their peer ports.
The system places the ports that cannot aggregate with the reference port in the Unselected state, for
example, as the result of the inter-board aggregation restriction.
When you configure static and dynamic aggregation modes, follow these guidelines:
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exceeded, places the ports with smaller port numbers in the Selected state and those with greater
port numbers in the Unselected state.
Places the member ports in the Unselected state if all the member ports are down.
Places the ports that cannot aggregate with the reference port in the Unselected state, for example,
as a result of the inter-board aggregation restriction.
The systems compare the system IDs. (A system ID contains the system LACP priority and the system
MAC address). The lower the LACP priority, the smaller the system ID. If LACP priority values are
the same, the two systems compare their system MAC addresses. The lower the MAC address, the
smaller the system ID.
The system with the smaller system ID chooses the port with the smallest port ID as the reference
port. (A port ID contains a port priority and a port number.) The port with the lower priority value
is chosen. If two ports have the same aggregation priority, the system compares their port numbers.
The port with the smaller port number becomes 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, the port
is placed in the Unselected state.
In an aggregation group, a Selected port must have the same port attributes and class-two
configurations as the reference port. To keep these configurations consistent, you should configure
the port manually.
Any port attribute or class-two configuration change might affect the aggregation state of all
member ports and ongoing traffic. If you need to make this change, make sure you understand its
impact on the live network.
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