NEC INTELLIGENT L2 SWITCH N8406-022A - Manual (Page 35)

Ports and trunking 35
Link Aggregation Control Protocol
Link Aggregation Control Protocol (LACP) is an IEEE 802.3ad standard for grouping several physical ports into one
logical port (known as a dynamic trunk group or Link Aggregation group) with any device that supports the standard.
Refer to the IEEE 802.3ad-2002 for a full description of the standard.
The 802.3ad standard allows standard Ethernet links to form a single Layer 2 link using the Link Aggregation
Control Protocol (LACP). Link aggregation is a method of grouping physical link segments of the same media type
and speed in full duplex, and treating them as if they were part of a single, logical link segment. If a link in a LACP
trunk group fails, traffic is reassigned dynamically to the remaining link(s) of the dynamic trunk group.
NOTE: Currently, LACP implementation does not support the Churn machine, an option used to detect if the
port is operable within a bounded time period between the actor and the partner. Only the Marker Responder
is implemented, and there is no marker protocol generator.
A port’s Link Aggregation Identifier (LAG ID) determines how the port can be aggregated. The Link Aggregation ID
(LAG ID) is constructed mainly from the system ID and the port’s admin key, as follows:
IMPORTANT: System ID—The system ID is an integer value based on the switch’s MAC address and the
system priority assigned in the CLI.
•
Admin key—A port’s Admin key is an integer value (1-65535) that you can configure in the CLI. Each switch
port that participates in the same LACP trunk group must have the same admin key value. The Admin key is
local significant, which means the partner switch does not need to use the same Admin key value.
For example, consider two switches, an Actor (this switch) and a Partner (another switch), as shown in the following
table:
Table 8 Actor vs. partner LACP configuration
Actor Switch Partner Switch 1 Partner Switch 2
Port 20 (admin key = 100) Port 1 (admin key = 50)
Port 21 (admin key = 100) Port 2 (admin key = 50)
Port 22 (admin key = 200) Port 3 (admin key = 60)
Port 23 (admin key = 200) Port 4 (admin key = 60)
In the configuration shown in the table above, Actor switch ports 20 and 21 aggregate to form an LACP trunk group
with Partner switch ports 1 and 2. At the same time, Actor switch ports 22 and 23 form a different LACP trunk group
with a different partner.
LACP automatically determines which member links can be aggregated and then aggregates them. It provides for
the controlled addition and removal of physical links for the link aggregation.
Each port in the switch can have one of the following LACP modes.
•
off (default)—The user can configure this port in to a regular static trunk group.
•
active—The port is capable of forming an LACP trunk. This port sends LACPDU packets to partner system
ports.
•
passive—The port is capable of forming an LACP trunk. This port only responds to the LACPDU packets sent
from an LACP active port.
Each active LACP port transmits LACP data units (LACPDUs), while each passive LACP port listens for LACPDUs.
During LACP negotiation, the admin key is exchanged. The LACP trunk group is enabled as long as the information
matches at both ends of the link. If the admin key value changes for a port at either end of the link, that port’s
association with the LACP trunk group is lost.
When the system is initialized, all ports by default are in LACP off mode and are assigned unique admin keys. To
make a group of ports aggregatable, you assign them all the same admin key. You must set the port’s LACP mode
to active to activate LACP negotiation. You can set other port’s LACP mode to passive, to reduce the amount of
LACPDU traffic at the initial trunk-forming stage.
Use the /info/l2/trunk command or the /info/l2/lacp/dump command to check whether the ports are
trunked.