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New Contributor III

Building VPC between FortiSwitches (MCLAG/ICL) and Cisco Nexus 9K Switches

I'm trying to bring up a trunk over a port-channel between a pair of 1048E's and a pair of Cisco 9504's that are configured using vPC.  One fibre connects one 1048 to one 9504, and the other fibre connects the other 1048 to the other 9504.  The VPC on the Cisco side fails, saying "vpc port channel mis-config due to vpc links in the 2 switches connected to different partners".  I am working with support and Cisco support, but I wanted to ask if others have gotten this working.  We're looking at possible spanning-tree issues, but also best practice guides on the Cisco side for VPC's.  I want to trunk my Fortinet distribution switches to my Cisco infrastructure so I can leverage other vlans in my Fortinet firewalls.  Any thoughts?

Esteemed Contributor III

I believe that error is when the vpc-peerlink does NOT carry the vlan tag btw. So in vPC if you have a vlan and the van is NOT over the vpc-peerlink, vPC creation will fail.


The following commands can be helpful;


  show vpc brief   show vpc peer   show port-channel summary   Ken Felix




PCNSE NSE StrongSwan
New Contributor

Hi seems you topology wrong,

  for FT to Cisco, your topology should be one FT channel to one Cisco switch,

you can not one FT channel to two Cisco switch.


New Contributor

I have a similar issue.

My setup contains 2 FortiSwitch 248D, managed via 2 FortiGate100Es. The two FortiSwitches are configures connected with a MCLAG-ICL link. I'm trying to connect my two FortiSwitches with my Cisco2960X (stacked as one logical switch) via LACP.

The LACP link goes does as soon as I connect the port from the second Fortiswitch to the LAG ports. On my Cisco switch, my ether-channel is err-dis. due to channel-misconfig (receiving BDPU's from a different sender).


Looking at my MCLAG link on the Fortiswitch, they should send LACP BDPU's with the same ID:


# diagnose switch mclag list

(*) - Using local system-id in LACP BPDU




    Local system ID              70:4c:a5:6f:37:4a

    Peer system ID               70:4c:a5:6f:37:4a

    Current system ID            70:4c:a5:6f:37:4a

    Local ports                  43-44

    Peer ports                   43-44

    Local uptime                 0 days  1h:16m: 3s

    Peer uptime                  0 days  0h: 0m: 0s

    Local LAG is configured as LACP active.

    Atleast one local LAG port is UP.

    Peer LAG is configured as LACP active

    All peer LAG ports are down,

    ICL traffic may be forwarded to local LAG port.

    Updates sent to peer         8108

    Updates received from peer   8105



# diagnose switch mclag list  

(*) - Using local system-id in LACP BPDU




    Local system ID              70:4c:a5:6f:2a:36

    Peer system ID               70:4c:a5:6f:37:4a

    Current system ID            70:4c:a5:6f:37:4a

    Local ports                  43-44

    Peer ports                   43-44

    Local uptime                 0 days  0h: 0m: 0s

    Peer uptime                  0 days  1h:14m:47s

    Local LAG is configured as LACP active.

    Peer system id is used in LACP BPDU.

    Peer LAG is configured as LACP active

    Atleast one peer LAG port is UP,

    local LAG ports are filtered for ICL traffic.

    Updates sent to peer         8030

    Updates received from peer   8033


I havn't been able to solve it yet. 

I really don't want to disable the channel-missconfig on my Cisco stack.




Is the mclag a trunk on the Fortiswitches?  What is going on with spanning tree?  I had to disable spanning tree on the mclag/trunk on my 1048's, that are ICL'd to each other.  Measure twice, cut once, when messing with spanning tree!  But for me, I had to disable that and the port-channel came up fine.  Also, if you are configuring in the GUI, click one one mclag member, hold control key, and then select the second member.  THEN right-click to disable STP.  I tried doing it to individual mclag members and it wasn't pretty.

New Contributor III

I have a PDF but cant attach.  Send me your email and I'll email to you.  I was able to build a LACP bundle but you need to follow the order of the instructions in the pdf.

Layer8 Consulting


Layer8 Consulting

Hi Huey,


    Please give me your instructions pdf.  I face the same issue with Cisco vPC with FS3032E MCLAG.



Wittaya J.


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