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Downstream LACP LAG device ports are blocked when connected to MLAG switch ports

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TitleDownstream LACP LAG device ports are blocked when connected to MLAG switch ports
Symptoms
  • No traffic passing through MLAG ports
  • LACP LAG ports on downstream device are removed from the port aggregation, no LACP adjacency is formed
  • VLANs that have LAG ports as members on downstream device block traffic on those ports
Environment
  • Summit X460
  • Summit Stack
  • EXOS 15.3.4.6
  • LACP
Cause
The downstream device LAG port was configured for LACP, but the remote MLAG port on the other side of the link is not.  This prevents an LACP adjacency from forming across the link and causes the LACP ports to be blocked.
Resolution
Configure the MLAG port facing the downstream device as LACP.  Enter the following command on the MLAG switch:
 
enable sharing <master port#> grouping <port list> algorithm lacp
 
Alternately, if you want to use static LAG links, you can configure the downstream switch LAG as a static LAG instead of LACP.  This will make both sides of the LAG link be static.
 
enable sharing <master port#> grouping <port list>
 
Additional notes
Make sure the LACP algorithm used is the same on both sides of the link.  The Extreme default algorithm is L2.

If one of the downstream LAG ports is blocked after enabling sharing on a MLAG port, create the load share group (LAG) first on the MLAG switch and then add the master port as the MLAG port.

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