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S2700, S3700, S5700, S6700, S7700, and S9700 Series Switches Interoperation and Replacement Guide

This document provides typical configuration examples for interoperation between Huawei switches and mainstream IP phones, firewalls, routers, Microsoft NLB servers, multi-NIC servers, Cisco switches, and SolarWinds.
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Overview of Ethernet Link Aggregation

Overview of Ethernet Link Aggregation


Ethernet link aggregation, also called Eth-Trunk, bundles multiple physical links to form a logical link to increase link bandwidth. The bundled links back up each other, increasing reliability.


As the network scale expands increasingly, users propose increasingly high requirements on Ethernet backbone network bandwidth and reliability. Originally, to increase the bandwidth, users use high-speed cards or devices supporting high-speed interface cards to replace old interface cards or devices. This solution, however, is costly and inflexible.

Link aggregation helps increase bandwidth by bundling a group of physical interfaces into a single logical interface, without upgrading the hardware. In addition, link aggregation provides link backup, greatly improving link reliability.

Link aggregation has the following advantages:

  • Increased bandwidth

    The bandwidth of the link aggregation interface is the sum of bandwidth of member interfaces.

  • Improved reliability

    When an active link fails, traffic on this active link is switched to another active link, improving reliability of the link aggregation interface.

  • Load balancing

    In a link aggregation group (LAG), traffic is load balanced among active links of member interfaces.

Classification of Link Aggregation

Link aggregation can work in manual load balancing mode or LACP mode depending on whether the Link Aggregation Control Protocol (LACP) is used.

  • Manual load balancing mode: You must manually create an Eth-Trunk and add member interfaces to the Eth-Trunk. In this mode, LACP is not required. This mode applies to the scenario where a high link bandwidth between two directly connected devices is required but the remote device does not support the LACP protocol.

  • LACP mode: In LACP mode, you also need to manually create an Eth-Trunk and add member interfaces to the Eth-Trunk. Active member interfaces are selected by sending LACP Data Units (LACPDUs) in LACP mode, which is different from the implementation in manual loading balancing mode. When a group of interfaces are added to an Eth-Trunk, they are classified into active and inactive ones by using LACPDUs. The LACP mode is also called the M:N mode, which implements both load balancing and link backup. M active links in the link aggregation group are responsible for forwarding and load balancing data, while the other N inactive links are backup ones and do not forward data. If an active link becomes faulty, the system selects the link with the highest priority from N inactive links. The inactive link becomes active and starts to forward data.

The implementation mechanisms of link aggregation in manual load balancing mode and LACP mode provided by different vendors are similar, and only commands and default settings are different.

Updated: 2019-05-15

Document ID: EDOC1000114005

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