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Two modes about configure LAG

Latest reply: Nov 27, 2018 13:28:53 401 1 1 0 0

LAG, link aggregation group, is a logical link formed by bundling several physical links.The logical port known as Eth-Trunk, has a lot of advantages, for example, increase the total bandwidth between two linked network equipments, offered a backup when few physical links down.

Link aggregation can work in manual mode or static LACP mode depending on whether LACP is used,

manual mode
In manual mode, Eth-Trunk should be created manually, also, adding member interfaces to the Eth-Trunk. Manual mode can be used when one of the linked network equipment doesn't support the LACP protocol.
Unlike in LACP mode, none maximum active-linknumber can be changed in a manual mode Eth-Trunk, which means no standby links exist, every active link will participate in traffic forwarding. On the contrary, least active-linknumber can be configured, this value will influence the minimum links that Eth-Trunk should have, when active links are smaller than it, the Eth-Trunk will turn to down state.

static LACP mode
In LACP mode, two linked network equipments send LACPDU to negotiating, determine which interfaces can be added to the Eth-Trunk, finally, form the Eth-Trunk.
During the negotiating, there is a few things we should notice.

  1. the device with the high priority(lower priority value) will determine which interfaces can be added to the Eth-Trunk, anohter device will add those interfaces that linked to the active interface on the opposite device to the Eth-Trunk. 
  2. If the total number of interfaces are more than the maximum active-linknumber which determine the maximum active interfaces, the device with the high priority(lower priority value) determine which interfaces are active interfaces by interface port priority, the rest interfaces are stanby, and when the one or more active interfaces turn to down state, the same amount of stanby interface will turn to active depending on their port priority. 

what is the advantages of static LACP mode compared with manual mode?
  static LACP mode can prevent some potetial configuring error.

when topology shows as below, 


when links between SW4 and SW5 are configured to Eth-Trunk, when using manual mode, on SW4, if both three ports are added in the Eth-Trunk, when server1 communicate with server2 some data traffic may be forwarded to server3, this will cause packet drops. Just like below picture show.
if static LACP mode is used, the linke between SW4 and SW6 wouldn't be selected for forwarding data, all the traffic will forwarded to SW5.


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Created Nov 27, 2018 13:28:53

The function of LAG is to increase the bandwidth between two devices and improve the efficiency of data transmission per unit time. It can be imagined that a swimming pool full of water, now to release the water, the installation of four drainpipe drainage is certainly faster than the installation of one drainpipe drainage, because the drainage per unit time is 4:1 relationship. So after using LAG, more data can be sent to the opposite end in unit time, and the operation efficiency of the business is higher.
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