H3C Technologies H3C S5560 Series Switches - Manual (Page 60)

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Aggregating links in dynamic mode
Dynamic aggregation mode is implemented through IEEE 802.3ad Link Aggregation Control Protocol
(LACP).
LACP
LACP uses LACPDUs to exchange aggregation information between LACP-enabled devices.
Each member port in an LACP-enabled aggregation group exchanges information with its peer. When a
member port receives an LACPDU, it compares the received information with information received on the
other member ports. In this way, the two systems reach an agreement on which ports are placed in the
Selected state.
LACP functions
LACP offers basic LACP functions and extended LACP functions, as described in Table 4 .
Table 4 Basic and extended LACP functions
Category Description
Basic LACP functions
Implemented through the basic LACPDU fields, including the system LACP priority,
system MAC address, port priority, port number, and operational key.
Extended LACP
functions
Implemented by extending the LACPDU with new TLV fields. This is how the LACP
MAD mechanism of the IRF feature is implemented.
The switch series can participate in LACP MAD as either an IRF member device or an
intermediate device.
For more information about IRF and the LACP MAD mechanism, see IRF
Configuration Guide.
LACP operating modes
LACP can operate in active mode or passive mode.
When LACP is operating in passive mode on a local member port and its peer port, both ports cannot
send LACPDUs. When LACP is operating in active mode on the port on either end of a link, both ports
can send LACPDUs.
LACP priorities
LACP priorities include system LACP priority and port priority, as described in Table 5 . The smaller the
priority value, the higher the priority.
Table 5 LACP priorities
Type Description
System LACP priority
Used by two peer devices (or systems) to determine which one is superior in link
aggregation.
In dynamic link aggregation, the system that has higher system LACP priority sets the
Selected state of member ports on its side. The system that has lower priority sets the
aggregation state of local member ports the same as their respective peer ports.
Port priority
Determines the likelihood of a member port to be selected on a system. A port with a
higher port priority is more likely to become Selected.