Dynamic Lacp Aggregation Group - 3Com WX3000 Series Operation Manual

Dynamic LACP Aggregation Group

Introduction to dynamic LACP aggregation group
A dynamic LACP aggregation group is automatically created and removed by the system. Users cannot
add/remove ports to/from it. A port can participate in dynamic link aggregation only when it is
LACP-enabled. Ports can be aggregated into a dynamic aggregation group only when they are
connected to the same peer device and have the same basic configuration (such as rate and duplex
mode).
Besides multiple-port aggregation groups, the system is also able to create single-port aggregation
groups, each of which contains only one port. LACP is enabled on the member ports of dynamic
aggregation groups.
Port status of dynamic aggregation group
A port in a dynamic aggregation group can be in one of the two states: selected or unselected. In a
dynamic aggregation group, both the selected and the unselected ports can transceive LACP protocol
packets; the selected ports can transceive user service packets, but the unselected ports cannot.
In an aggregation group, the selected port with the smallest port number serves as the master port of
the group, and other selected ports serve as member ports of the group.
There is a limit on the number of selected ports in an aggregation group. Therefore, if the number of the
member ports that can be set as selected ports in an aggregation group exceeds the maximum number
supported by the device, the system will negotiate with its peer end, to determine the states of the
member ports according to the port IDs of the preferred device (that is, the device with smaller system
ID). The following is the negotiation procedure:
1) Compare device IDs (system priority + system MAC address) between the two parties. First
compare the two system priorities, then the two system MAC addresses if the system priorities are
equal. The device with smaller device ID will be considered as the preferred one.
2) Compare port IDs (port priority + port number) on the preferred device. The comparison between
two port IDs is as follows: First compare the two port priorities, then the two port numbers if the two
port priorities are equal; the port with the smallest port ID is the selected port and the left ports are
unselected ports.
Configuring system priority
LACP determines the selected and unselected states of the dynamic aggregation group members
according to the priority of the port ID on the end with the preferred device ID.
The device ID consists of two-byte system priority and six-byte system MAC address, that is, device ID
= system priority + system MAC address.
When two device IDs are compared, the system priorities are compared first, and the system MAC
addresses are compared when the system priorities are the same. The device with smaller device ID
will be considered as the preferred one.
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