Adding new VM to VLAN in vSphere drops connection on running VM

Posted by Fair-Wolf-9024@reddit | sysadmin | View on Reddit | 10 comments

Hello, everyone!

I am junior sysadmin, 1.5 month since started working. I faced this problem: on a test host (installed on HP ProLiant DL360 Gen8) we have own server with LLM running for our organization's database team. Today I was given a task to deploy on that same host Windows11 machine to install all necessary software to make a golden template from that win11 machine. So basically that ESXi host was supposed to have two VMs (LLM and my Win11). The thing is that I deployed this win11 machine and configured network (ip, dns, gateway) in windows itself and placed VM in the correct subnet but as soon as I connect this the VM to the necessary VLAN in vCenter UI any connection on LLM machine drops. Moreover, these two VMs exchange their MAC addresses between each other and now neither of them have connection. Network team member told me that this problem is not on their side. The hardware in server room seems to work correct too. Could someone give a hint at what level of abstraction or segment the troubleshooting of this problem lies? I would appreciate any help. Hope to solve this problem before DBA team notices that their llm cannot fetch info from their databases :)

Thanks in advance.

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Expensive-Rhubarb267@reddit

How did you deploy the Windows 11 VM? If you've got 2 devices in the same broadcast domain with a duplicate MAC address then they'll clash & you'll have a bad time.

It sounds like you're LLM VM has it's vNIC set to manual & you cloned the VM. In that case, as far as your network is concerned those 2 VMs are exactly the same.

Bin off the Windows 11 VM & create a new one from scratch - using a .iso, not by clueing an existing VM.

genisthebest@reddit

you could also just delete the adapter for the win 11 vm and add a new one. that should make sure the MAC is different. you find that under edit settings of the vm.

PlayfulSolution4661@reddit

If you’re using different VLANs on the same NIC, you may need to add a native VLAN for traffic to get tagged properly. I was doing something similar recently and needed to add the native VLAN on the Cisco switch side for it to work properly on VMware. Native vlan can be whatever you just need to set it so VMware knows it should tag traffic and vlan traffic can flow

agana49@reddit

Could be this: If vm is cloned from the same template as llm vm, they could have same MAC leading to ARP table corruption.

Check the network adapter of each VM, and if there are duplicates, you can manually enter a mac or delete re-add network adapter.

Clear ARP on LLM, maybe on switch too.

dvr75@reddit

What's configured on the Vswitch Load Balancing?

Fair-Wolf-9024@reddit (OP)

route based on originating virtual port

each Vlan has virtual port assigned?
Does the virtual port has different Load Balance policy?

DueAbbreviations4731@reddit

Please provide more detail on the VLAN settings of each VM NIC, vswitch or distributed switch config, and your host to LAN connectivity info. Are you running trucked ports or access ports?

I am using vss; vmnic is up until i add win11 vm to necessary vlan. then vmnic goes down and I have to ask network admin to drop configs on it so it will go up again. We are running trunk ports.