Description

This article explains what happens when the Link Aggregation Control Protocol (LACP) force-up knob is enabled in a multichassis link aggregation group (MC-LAG) environment on QFX10002 devices when the server side does not support LACP.

 

Symptoms

When the force-up option is configured in QFX10002 devices, you will see the LACP state as Collecting & Distributing only on Switch-1, whereas it shows as Attached on the other MC-LAG switch, that is Switch-2.

Output 

root@Switch-1# run show lacp interfaces 
Aggregated interface: ae1
    LACP state:       Role   Exp   Def  Dist  Col  Syn  Aggr  Timeout  Activity
      xe-0/0/0 FUP    Actor   No    No   Yes  Yes  Yes   Yes     Fast    Active
      xe-0/0/0 FUP  Partner   No   Yes    No   No  Yes   Yes     Fast   Passive
    LACP protocol:        Receive State  Transmit State          Mux State 
      xe-0/0/0 FUP              Current   Fast periodic Collecting distributing

root@Switch-2# run show lacp interfaces 
Aggregated interface: ae1
    LACP state:       Role   Exp   Def  Dist  Col  Syn  Aggr  Timeout  Activity
      xe-0/0/0 FUP    Actor   No    No   No  No  Yes   Yes     Fast    Active
      xe-0/0/0 FUP  Partner   No   Yes    No   No  Yes   Yes     Fast   Passive
    LACP protocol:        Receive State  Transmit State          Mux State 
      xe-0/0/0               Current   Fast periodic            Attached

 

Solution

In the above MC-LAG setup, when the server does not have LACP support, configuring the force-up knob on any one interface of the AE bundle would help bring the LACP state to Collecting & Distributing on all the interfaces in the LAG on both the MC-LAG peers. 

root@Switch-1# set interfaces xe-0/0/0 ether-options 802.3ad lacp force-up << This would bring LACP up on both peers.

This has been explained in more detail in Forcing MC-LAG Links or Interfaces with Limited LACP Capability to Be Up .

However, in the case of QFX10002 devices, this force-up knob for LACP is not supported when it is used along with MC-LAG.

 

It is recommended not to use the force-up option if QFX10002 devices are in use.