H3C Technologies H3C S3100 Series Switches - Manual (Page 156)

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Link Aggregation Configuration
Overview
Introduction to Link Aggregation
Link aggregation can aggregate multiple Ethernet ports together to form a logical aggregation group. To
upper layer entities, all the physical links in an aggregation group are a single logical link.
Link aggregation is designed to increase bandwidth by implementing outgoing/incoming load sharing
among the member ports in an aggregation group. Link aggregation group also allows for port
redundancy, which improves connection reliability.
Introduction to LACP
The IEEE 802.3ad Link Aggregation Control Protocol (LACP) enables the dynamic aggregation of
physical links and The Link Aggregation Control Protocol (LACP) is defined in IEEE 802.3ad. It uses link
aggregation control protocol data units (LACPDUs) for information exchange between LACP-enabled
devices. With the usage of preserved 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 ports should be With LACP
enabled on a port, LACP notifies the following information of the port to its peer by sending LACPDUs:
priority and MAC address of this system, priority, number and operation key of the port. Upon receiving
the information, the peer compares the information with the information of other ports on the peer
device to determine the ports that can be aggregated. In this way, the two parties can reach an
agreement in added/removed to/from a dynamic aggregation group.
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) stack.