Link Aggregation; Overview - 3Com 7757 Configuration Manual

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Overview

Introduction to Link
Aggregation
Introduction to LACP
L A
INK GGREGATION
Link aggregation aggregates multiple physical Ethernet ports into one logical link,
also called an aggregation group. It allows you to increase bandwidth by
distributing incoming/outgoing traffic on the member ports in the aggregation
group. In addition, it provides reliable connectivity because these member ports
can dynamically back up each other.
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.
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.
The purpose of the link aggregation control protocol (LACP) is to implement
dynamic link aggregation and deaggregation. This protocol is defined in
IEEE802.3ad. It uses link aggregation control protocol data units (LACPDUs) for
information exchange between LACP-enabled devices.
After LACP is enabled on a port, the port sends LACPDUs to notify the remote
system of its system LACP priority, system MAC address, port LACP priority, port
number, and operational key. Upon receipt of an LACPDU, the remote system
compares the received information with the information received on other ports to
determine the ports that can operate as selected ports. This allows the two
systems to reach an agreement on the states of the related ports.
C
ONFIGURATION