I am trying to figure out how to configure both MSTP for the core network and if I will need to enable MSTP on VDX6740 for this diagram after adding the new datacenter switches:


Diagram link: https://ibb.co/9W4tdHs

I have the following questions:

  1. Concerning vLAG, is the way I am connecting VDX to the core stack correct?
  2. Concerning MSTP, is it OK if I use instance 0 for all vlans? What is the recommended scenario in this case? I have 100 VLANs.
  3. Should I use MSTP for VDX switches assuming my vLAG connections are correct?
  4. I need help with a sample configuration for VDX vLAGs with KCX stack with MSTP enabled on that stack to grasp how I should configure my new VDX switches. According to my humble knowledge, the ICX stack needs to see both VDX switches from the two vLAGs as one VDX switch, I am really confused, plz I need help.

If you guys need more info plz ask.

thank you

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    Dec 25, 2018 at 10:12

1 Answer 1


If your ICXs are stacked and the VDXs are operating as a VCS, they will each be logically seen as a single device to STP, so you could potentially combine all four links into a single vLAG. The advantage would be that STP would see a single link. There would be no redundant path to block. You would then not need to use MSTP load balancing which adds complexity to a network.

If you do use MSTP, it is best practice to not use instance 0.

If you do go with the dual vLAG scenario, you could add half the VLANs to instance 1 and half to instance 2, then manipulate the STP costs for each instance so that the VCS selects a different root port for each instance. One vLAG would be forwarding for one instance and the other vLAG would be forwarding for the other instance. The single vLAG option is much simpler though.

  • I have tried what you are suggesting. I noticed that the ICX stack sees two different VDXs although they are configured as VCS, I don't know why. I must dig deeper into it to see why my cores are seeing two VDX MACs instead of one..
    – elekgeek
    Dec 1, 2018 at 21:56

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