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How do VMs react when uplinks do not contain the same vLANs?

  • 1.  How do VMs react when uplinks do not contain the same vLANs?

    Posted Feb 27, 2025 09:19 PM

    Let me explain what I'm thinking. If I have 4 uplinks connected to one VDS, however uplinks 1 & 2 have vLAN01 & vLAN02 and uplinks 3 & 4 only have vLAN03 & vLAN04 and I have 4 VMs connected to the VDS switch with VM01 connected to vLAN01, VM02 connected to vLAN02, VM03 connected to vLAN03 and VM04 connected to vLAN04.

    Is vCenter smart enough to route traffic for VM01 & VM02 thru uplinks 1 & 2 and traffic for VM03 & VM04 thru uplinks 3 & 4? Or will I see VMs dropping off the network as they are "blindly" routed to an uplink which does not contain their vLAN?

    My situation:

    I currently have vCenter 7 configured with VDS, NSX-T 3.2 configured with NVDS and am planning an "NVDS-to-VDS" migration and am trying to figger out how to set this up switch-wise.

    I understand that the NVDS migration will result in a new VDS switch being created in vCenter.

    After the migration, I want to reduce the number of VDS switches- should I just leave the new NVDS-VDS switch with it's current uplinks as-is?

    I know VDS supports DV Port Groups and also NSX Port Groups- can I migrate the VMs on the newly created NVDS-VDS switch to the existing DVS switch after the migration? I understand that the vLANs currently available on the NVDS switch will have to be presented to the DVS switch for this to work. I assume that VMs (and thus vLANs) on the NVDS-DVS switch will still be able to communicate with the VMs (and thus the same vLANs) on the DVS switch which should give me the ability to migrate VMs from the NVDS-DVS to the DVS switches.

    If there are no red flags up to this point, I would then consider moving the NVDS-DVS uplinks to the DVS switch (thus changing the number of uplinks on the DVS switch from 2 to 4) and finally decom the NVDS-DVS switch.

    Do you think this will work? 



  • 2.  RE: How do VMs react when uplinks do not contain the same vLANs?

    Posted Feb 28, 2025 09:50 AM
    Edited by MikeDawson Feb 28, 2025 09:50 AM

    I have no experience with NSX or NVDS, however with a virtual distributed switch, if your portgroups are set to use all uplinks, and some of those uplinks are missing VLANs, your VMs will drop off the network if their traffic ends up getting routed to those vmnics due to the load balancing protocol you have selected.  You can edit each port group manually and move the uplinks that are missing the VLANs down to "Unused" if you need to

    Also keep in mind that you can enable a health check on your Distributed vSwitch, and it will light up every VLAN that is missing 


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