3Com 4210G Series Configuration Manual page 53

Selected: a selected port can forward user traffic.
Unselected: an unselected port cannot forward user traffic.
The rate of an aggregate interface is the sum of the selected member ports' rates. The duplex mode of
an aggregate interface is consistent with that of the selected member ports. Note that all selected
member ports use the same duplex mode.
For how the state of a member port is determined, refer to
aggregation mode.
IEEE 802.3ad LACP protocol
The IEEE 802.3ad Link Aggregation Control Protocol (LACP) enables the dynamic aggregation of
physical links and uses link aggregation control protocol data units (LACPDUs) for information
exchange between LACP-enabled devices. With the usage of expansion fields in LACPDUs, LACP
can deliver extended functions in addition to its basic functions.
1) Basic LACP functions
Basic LACP functions are achieved with the basic fields in LACPDUs, which cover information
including system LACP priority, system MAC address, port LACP priority, port number, and operational
key. With LACP enabled on a port, LACP sends the above information of the port to its peer via
LACPDUs. Upon receiving an LACPDU, the peer compares the received information with the
information received on other ports. This allows the two systems to reach an agreement on which link
aggregation member ports should be placed in the selected state.
2) Extended LACP functions
By using expansion fields in LACPDUs, you can expand the functions of LACP. For example, by
defining a new Type/Length/Value (TLV) data field among the expansion fields of the LACPDUs, you
can deliver the LACP multi-active detection (MAD) mechanism in an Intelligent Resilient Framework
(IRF).
Switches of the Switch 4210G Family that support extended LACP functions can function as both
member devices and intermediate devices in LACP MAD implementation.
For details about IRF, member devices, intermediate devices, and the LACP MAD mechanism,
see IRF in the System Volume.
Marker protocol
During a session, if member ports are added to or removed from a dynamic link aggregation group,,
service traffic will need to be redistributed among all the new member ports of the link aggregation
group. The Marker protocol can be employed to quickly redistribute service traffic within link
aggregation groups and ensure the orderly transmission of data frames. The process is as follows:
The device stops transmitting service traffic and starts a timer during which no data frames will
be transmitted on the links.
The local end uses the Marker protocol to send a Marker Protocol Data Unit (PDU).
Static aggregation mode
2-2
and Dynamic