Allied Telesis AT-S63 - Manual (Page 83)

AT-S63 Management Software Features Guide
Section I: Basic Operations 83
Overview
LACP (Link Aggregation Control Protocol) port trunks perform the same
function as static trunks. They increase the bandwidth between network
devices by distributing the traffic load over multiple physical links. The
advantage of an LACP trunk over a static port trunk is its flexibility. While
implementations of static trunking tend to be vendor specific, the
implementation of LACP in the AT-S63 Management Software is
compliant with the IEEE 802.3ad standard, making it interoperable with
equipment from other vendors that also comply with the standard.
Therefore, you can create an LACP trunk between an Allied Telesis device
and network devices from other manufacturers.
Another advantage is that ports in an LACP trunk can function in a standby
mode. This adds redundancy and resiliency to the trunk. If a link in a static
trunk goes down, the overall bandwidth of the trunk is reduced until the link
is reestablished or another port is added to the trunk. In contrast, an LACP
trunk can automatically activate ports in a standby mode when an active
link fails so that the maximum possible bandwidth of the trunk is
maintained.
For example, assume you create an LACP trunk of ports 11 to 20 on a
switch and the switch is using ports 11 to 18 as the active ports and ports
19 and 20 as reserve. If an active port loses its link, the switch
automatically activates one of the reserve ports to maintain maximum
bandwidth of the trunk.
The main component of an LACP trunk is an aggregator. An aggregator is
a group of ports on the switch. The ports in an aggregator are further
grouped into one or more trunks, referred to as aggregate trunks.
An aggregate trunk can consist of any number of ports on a switch, but
only a maximum of eight ports can be active at a time. If an aggregate
trunk contains more ports than can be active at one time, the extra ports
are placed in a standby mode. Ports in the standby mode do not pass
network traffic, but they do transmit and accept LACP data unit (LACPDU)
packets, which the switch uses to search for LACP-compliant devices.
Only ports on a switch that are part of an aggregator transmit LACPDU
packets. If a switch port that is part of an aggregator does not receive
LACPDU packets from its corresponding port on the other device, it
assumes that the other port is not part of an LACP trunk. Instead, it
functions as a normal Ethernet port by forwarding network traffic.
However, it does continue to send LACPDU packets. If it begins to receive
LACPDU packets, it automatically transitions to an active or standby mode
as part of an aggregate trunk.