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Borys_DE
Borys_DE
Explorer II
July 24, 2025
Solved

Configuration MCLAG between Fortiswitches and Aruba

  • July 24, 2025
  • 2 replies
  • 1838 views

Hallo everyone. 

I recently started working for a company that has this network topology.

network_topology.png

I see that the Aruba switches are set to MСLAG with Fortiswitches, but from the Fortiswich side there are no MCLAG settings. At the same time, Fortiswiches are online and available through Fortigate. 

I tried to set up MСLAG on FortiSwitch, but I encountered the fact that the Aruba side is specified as native VLAN 4094, and there is no such VLAN on FortiSwitches, at least I don’t see it through Fortigate GUI.
Should I create a new VLAN with ID 4094 or is it better to change the native VLAN on Aruba?
I am confused that VLAN with ID 4094 is specified everywhere in Aruba settings as native and the network works.

    Best answer by fricci_FTNT

    Hi @Borys_DE ,

    Correct, if one of the Aruba switches dies, the spanning tree will be recalculated and the traffic will go through the other Aruba switch.

     

    Best regards,

    2 replies

    ebilcari
    Staff
    ebilcari
    Staff
    July 24, 2025

    VLAN 4094 is dedicated for FortiLink, you can try to change it in the Aruba or in the Fortiswitches.

    Some details are shown here: Troubleshooting Tip: Change FortiLink management vlan from 4094 to customized management VLAN

    Emirjon
      fricci_FTNT
      Staff
      fricci_FTNT
      Staff
      July 24, 2025

      Hi @Borys_DE ,

       

      You do not see VLAN 4094 on FortiGate GUI because it is the default management VLAN for managed FortiSwitches.
      Regarding your question:
      >>"Should I create a new VLAN with ID 4094 or is it better to change the native VLAN on Aruba?"
      I would not change it and would leave it as it is.
      From the FortiSwitch CLI you can check the default management VLAN with "show switch auto-network".

      Are the Aruba switches directly connected by a LAG or single port? From the diagram they do not seem to be directly connected.

      For a MCLAG configuration you can check the following documentation:
      https://docs.fortinet.com/document/fortiswitch/7.2.8/administration-guide/860027/mclag

      Please keep in mind that making MCLAG changes on the FortiSwitches might create brief network disruptions.
       
      Best regards,

        Borys_DE
        Borys_DEAuthor
        Explorer II
        July 25, 2025

        Hi,

        Here are the settings on each Aruba switch:
         
        "interface lag 11 multi-chassis
        description FTG1_X1_X2
        no shutdown
        no routing
        vlan trunk native 4094
        vlan trunk allowed 5,11,21,31,41,110,130,140,150,170,180,1606,1610,2110,2168,2505,2550,2998,4042,4047,4083,4088-4094
        lacp mode active
        spanning-tree port-type admin-edge
        interface lag 12 multi-chassis
        description FTG2_X1_X2
        no shutdown
        no routing
        vlan trunk native 4094
        vlan trunk allowed 5,11,21,31,41,110,130,140,150,170,180,1606,1610,2110,2168,2505,2550,2998,4042,4047,4083,4088-4094
        lacp mode active
        spanning-tree port-type admin-edge
        interface lag 21 multi-chassis
        description FSw1_P51_P52
        no shutdown
        no routing
        vlan trunk native 4094
        vlan trunk allowed 5,11,21,31,41,110,130,140,150,170,180,1606,1610,2110,2168,2505,2550,2998,4042,4047,4088-4094
        lacp mode active
        spanning-tree root-guard
        interface lag 22 multi-chassis
        description FSw2_P51_P52
        no shutdown
        no routing
        vlan trunk native 4094
        vlan trunk allowed 5,11,21,31,41,110,130,140,150,170,180,1606,1610,2110,2168,2505,2550,2998,4042,4047,4088-4094
        lacp mode active
        spanning-tree root-guard
        interface lag 23 multi-chassis
        description FSw3_P51_P52
        no shutdown
        no routing
        vlan trunk native 4094
        vlan trunk allowed 5,11,21,31,41,110,130,140,150,170,180,1606,1610,2110,2168,2505,2550,2998,4042,4047,4088-4094
        lacp mode active
        spanning-tree root-guard
        interface lag 24 multi-chassis
        description FSw4_P51_P52
        no shutdown
        no routing
        vlan trunk native 4094
        vlan trunk allowed 5,11,21,31,41,110,130,140,150,170,180,1606,1610,2110,2168,2505,2550,2998,4042,4047,4088-4094
        lacp mode active
        spanning-tree root-guard"
         
        As I understand it, both Fortigates and FortiSwitches are connected to Aruba via MCLAG. But the lack of any settings on the FortiSwitches side confuses me. MCLAG must be configured on both sides, otherwise it simply does not work.
         

         

          fricci_FTNT
          Staff
          fricci_FTNT
          Staff
          July 25, 2025

          Hi @Borys_DE ,

           

          Regarding your doubt:
          >>"But the lack of any settings on the FortiSwitches side confuses me. MCLAG must be configured on both sides, otherwise it simply does not work."
          If you want to have MCLAG from the point-of-view of the FortiSwitches towards the Aruba, then yes, you have to configure them on FortiSwitches as well. If MCLAG is not configured on FortiSwitches towards the Aruba, the traffic will flow according to the spanning tree.
          Hope this helps.


          Best regards,

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