The Link Aggregation Control Protocol (LACP) can improve fault tolerance of the Eth-Trunk,
provide backup, and ensure high reliability of member links.
LACP uses a standard negotiation mechanism for a switching device so that the switching device
can create and start the aggregated link based on its configuration. After the aggregated link is
created, LACP maintains the link status. If an aggregated link's status changes, LACP adjusts
or removes the link.
For example, in
, four interfaces on DeviceA are bundled into an Eth-Trunk and the
Eth-Trunk is connected to the corresponding interfaces on DeviceB. Because an interface on
DeviceA is incorrectly connected to an interface on DeviceC, DeviceA may incorrectly send
data destined for DeviceB to DeviceC. However, the Eth-Trunk in manual load balancing mode
cannot detect this fault in a timely manner.
If LACP is enabled on DeviceA and DeviceB, the Eth-Trunk correctly selects active links to
forward data after negotiation. Data sent by DeviceA can reach DeviceB.
Figure 2-3
Incorrect Eth-Trunk connection
DeviceC
DeviceA
DeviceB
Eth-Trunk
Concepts
l
LACP system priority
LACP system priorities are set on devices at both ends of an Eth-Trunk. In LACP mode,
active member interfaces selected by both devices must be consistent; otherwise, an LAG
cannot be established. To keep active member interfaces consistent at both ends, set a higher
priority for one end so that the other end selects active member interfaces based on the
selection of the end with a higher priority. The smaller the LACP system priority value,
the higher the LACP system priority.
l
LACP interface priority
Interface LACP priorities are set to prioritize interfaces of an Eth-Trunk. Interfaces with
higher priorities are selected as active interfaces. The smaller the LACP interface priority
value, the higher the LACP interface priority.
l
M:N backup of member interfaces
In LACP mode, LACP is used to negotiate parameters to determine active links in an LAG.
This mode is also called the M:N mode, where M refers to the number of active links and
N refers to the number of backup links. This mode guarantees high reliability and allows
traffic to be load balanced among M active links.
As shown in
, M+N links with the same attributes (in the same LAG) are set up
between two devices. When data is transmitted over the aggregated link, traffic is load
balanced among M active links and no data is transmitted over N backup links. Therefore,
the actual bandwidth of the aggregated link is the sum of the M links' bandwidth, and the
maximum bandwidth of the aggregated link is the sum of the M+N links' bandwidth.
Huawei AR530&AR550 Series Industrial Switch Routers
Configuration Guide - Ethernet Switching
2 Link Aggregation Configuration
Issue 01 (2014-11-30)
Huawei Proprietary and Confidential
Copyright © Huawei Technologies Co., Ltd.
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