Handbook

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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 2 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 18 (admin key = 100)
Port 1 (admin key = 50)
Port 19 (admin key = 100)
Port 2 (admin key = 50)
Port 20 (admin key = 200)
Port 3 (admin key = 60)
Port 21 (admin key = 200)
Port 4 (admin key = 60)
In the configuration shown in the table above, Actor switch ports 18 and 19 aggregate to form an LACP
trunk group with Partner switch ports 1 and 2. At the same time, Actor switch ports 20and 21 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.