Allied Telesis AT-S63 - Manual (Page 150)

Chapter 8: Static and LACP Port Trunks
150 Section I: Basic Features
ˆ The switch can support up to six static and LACP trunks at a time (for
example, four static trunks and two LACP trunks). An LACP trunk is
countered against the maximum number of trunks only when it is
active.
ˆ The switch selects the lowest numbered port in the trunk to handle
broadcast packets and packets of unknown destination. For example,
a trunk of ports 11 to 15 would use port 11 for broadcast packets.
LACP Trunk
Overview
An LACP (Link Aggregation Control Protocol) trunk is another type of port
trunk. It performs the same function as a static trunk. It increases the
bandwidth between two 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
AT-9400 Series implementation of LACP is compliant with the IEEE
802.3ad standard. This makes it interoperable with equipment from other
vendors that also comply with the standard. Therefore, you can create an
LACP trunk between an Allied Telesyn device and networking 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
and restoring it requires reestablishing the link or manually modifying the
trunk by adding another port to it. In contrast, an LACP trunk can activate
ports in a standby mode when an active link fails. The automatic activation
of standby ports allows the switch to maintain the maximum possible
bandwidth of the trunk.
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 two 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