3Com Switch 7750 Configuration Guide Guide

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LINK AGGREGATION CONFIGURATION
Overview
Introduction to Link
Aggregation
Link aggregation means aggregating several ports together to form an
aggregation group, so as to implement outgoing/incoming load sharing among
the member ports in the group and to enhance the connection reliability.
Depending on different aggregation modes, aggregation groups fall into three
types: manual, static LACP, and dynamic LACP. Depending on whether or not load
sharing is implemented, aggregation groups can be load-sharing or
non-load-sharing aggregation groups.
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Up to 384 aggregation groups can be created in a system, where up to 64
load-sharing aggregation groups can be created.
For the member ports in an aggregation group, their basic configuration must be
the same. The basic configuration includes STP, QoS, VLAN, port attributes and
other associated settings.
■ STP configuration, including STP status (enabled or disabled), link attribute
(point-to-point or not), STP priority, maximum transmission speed, loop
prevention status, root protection status, edge port or not.
■ QoS configuration, including traffic limiting, priority marking, default 802.1p
priority, bandwidth assurance, congestion avoidance, traffic redirection, traffic
statistics, and so on.
■ VLAN configuration, including permitted VLANs, and default VLAN ID.
■ Port attribute configuration, including port rate, duplex mode, and link type
(Trunk, Hybrid or Access). The ports for a manual or static aggregation group
must have the same link type, and the ports for a dynamic aggregation group
must have the same rate, duplex mode and link type.
Introduction to LACP The purpose of link aggregation control protocol (LACP) is to implement dynamic
link aggregation and deaggregation. This protocol is based on IEEE802.3ad and
uses LACPDUs (link aggregation control protocol data units) to interact with its
peer.
After LACP is 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 with the receiving port.
In this way, the two parties can reach an agreement in adding/removing the port
to/from a dynamic aggregation group.