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LACP mode for Link Aggregation

Latest reply: Jun 12, 2019 07:20:25 493 2 1 0

The Link Aggregation Control Protocol (LACP) is an aggregation mode which can improve fault tolerance of the Eth-Trunk and ensure high reliability of the member links. LACP uses a standard negotiation mechanism for switching devices, ensuring that switching devices automatically create and enable aggregated links based on their configurations. After aggregated links are created, LACP maintains link status. If an aggregated link's status changes, LACP automatically adjusts or disables the link.

LACP system priorities are set on devices at both ends of a trunk link. In LACP mode, active member interfaces selected by both devices must be consistent; otherwise, the LAG (Link Aggregation Group) cannot be established. To keep active member interfaces consistent at both ends, set a higher priority for one end. In this manner, the other end selects active member interfaces based on the selection of the peer. The smaller the LACP system priority value, the higher the LACP system priority.

The LACP interface priority is set for a member interface to determine whether it can be selected as an active member interface. The smaller the LACP interface priority value, the higher the LACP interface priority.

In LACP mode, LACP is used to negotiate parameters to determine active member 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 load balancing to be carried out across M active links.

If one of the M links fails, LACP selects a link from the N backup links to replace the faulty link. In such a situation, the actual bandwidth of the aggregated link is still the sum of M links' bandwidth, the maximum bandwidth of the aggregated link, however, becomes the sum of the M+N-1 links' bandwidth.


You can find below a case example for the LACP mode: 



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Created Jun 11, 2019 16:48:23 Helpful(0) Helpful(0)

Great share, keep it up!
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Created Jun 12, 2019 07:20:25 Helpful(0) Helpful(0)

Hello Guys!
Just a little addition the the nice post from @MarkP :
If you configure "max active-linknumber " value which is lower than actual physical ports in the Eth-trunk, it is suggested to use LACP priority for physical interface to control which interface will not be selected in Eth-trunk and LACP preemption to control when we can re-use our old Eth-trunk link member.

Interface Gig 0/0/22
lacp priority 1
lacp preempt enable
lacp preempt delay 15

Interface Gig 0/0/23
lacp priority 2
lacp preempt enable
lacp preempt delay 15

Interface Gig 0/0/24
lacp priority 100

Take care, Guys!
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