Configuring link aggregation and LACP
Overview
Link aggregation aggregates multiple physical Ethernet ports into one logical link, also called an
aggregation group.
It allows you to increase bandwidth by distributing traffic across the member ports in the aggregation
group. In addition, it provides reliable connectivity because these member ports can dynamically back
up each other.
Basic concepts
Aggregation group, member port, and aggregate interface
Link aggregation is implemented by combining Ethernet interfaces (call member ports) into a link
aggregation group. Each link aggregation group has one logical aggregate interface.
When you create an aggregate interface, the switch automatically creates an aggregation group of the
same type and number as the aggregate interface. For example, when you create interface
Bridge-Aggregation 1, Layer 2 aggregation group 1 is automatically created.
The rate of an aggregate interface equals the total rate of its member ports in Selected state, and its
duplex mode is the same as the selected member ports.
States of the member ports in an aggregation group
A member port in an aggregation group can be in one of the following states:
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. All selected member ports
use the same duplex mode.
For how the state of a member port is determined, see
aggregation
LACP protocol
The Link Aggregation Control Protocol (LACP) is defined in IEEE 802.3ad. It uses LACPDUs for
information exchange between LACP-enabled devices.
LACP is automatically enabled on interfaces in a dynamic aggregation group. For information about
dynamic aggregation groups, see
LACPDUs to notify the remote system (the partner) of its system LACP priority, system MAC address, LACP
port priority, port number, and operational key. Upon receiving an LACPDU, the partner compares the
received information with the information received on other interfaces to determine the interfaces that
can operate as Selected interfaces. This allows the two systems to reach an agreement on which link
aggregation member ports should be placed in Selected state.
mode."
"Dynamic aggregation
180
"Static aggregation
mode" and
mode." An LACP-enabled interface sends
"Dynamic