If one of M links fails, LACP selects a link from N backup links to replace the faulty link.
The actual bandwidth of the aggregated link is still the sum of M links' bandwidth, but the
maximum bandwidth of the aggregated link is the sum of the (M+N-1) links' bandwidth.
Figure 2-4 Networking of M:N backup
DeviceA
DeviceB
Eth-Trunk 1 Eth-Trunk 1
Eth-Trunk
Active link
Backup link
M:N backup is mainly applied in situations where the bandwidth of M links must be assured
and a fault tolerance mechanism is in place. If an active link fails, the system selects the
backup link with the highest priority as the active link.
If no available backup link is found and the number of active links is smaller than the lower
threshold for the number of active interfaces, the system shuts down the LAG.
Implementation of Link Aggregation in LACP Mode
LACP, as specified in IEEE 802.3ad, implements dynamic link aggregation and de-aggregation,
allowing both ends to exchange LACPDUs.
After member interfaces are added to an Eth-Trunk in LACP mode, each end sends LACPDUs
to inform its remote end of its system priority, MAC address, member interface priorities,
interface numbers, and keys. The remote end then compares this information with that saved on
itself, and selects which interfaces to be aggregated. The two ends perform LACP negotiation
to select active interfaces and links.
Figure 2-5 shows the format of an LACPDU.
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.
35
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