[SOLVED] Network goes down after starting up a virtual machine

[joel-prox]

Hello,

I am new to PROXMOX and want to try to set up my first VM.

Setup: I have two old DELL OptiPlex 7050 Micro to start with. Here some hardware details, if they are relevant:
https://www.dell.com/support/produc.../0-QkUzSWRReTgzd21odkpuZGlmMnhodz090/overview

Router is an Unifi Dream Machine Pro. I use a VLAN (192.168.2.x) for Proxmox Nodes. After the installation of a node, it gets the static IP 192.168.2.11.


So far so good.

After creating my first VM (e. g. debian 13), upon booting the VM, the node is no longer accessible (neither SSH nor web gui). Here is the IP A, if that is helpful.



The VM gets an IP from my router within the 192.168.2.x range. But the node is not accessible.

As soon as I stop the VM via console, the node is accessible again. I do not know, what to do our change. I found a relating article to this:
https://pve.proxmox.com/wiki/PCI_Passthrough
But sinceI do not use any PCI or networking, that does not seem relevant for my case. The other forum articles were not helpful either (e. g. https://forum.proxmox.com/threads/web-gui-not-working.125693/).

Can anyone point my in the right direction? That would me most appreciated. Thanks!

Best regards
Joel

 

[Onslow]

You wrote:

The VM gets an IP from my router within the 192.168.2.x range.

Which, precisely, IP address does the VM get?

The symptom is similar to an IP address conflict.
Maybe the DHCP server gives the same IP address that PVE host is using?
What is the DHCP range?

 

[joel-prox]

The new VM has 192.168.2.28.
Yes it sound like IP conflict, but no other device on my router has either this IP, nor the IP of the proxmox node nor of my client.
The DHCP range is 192.168.2.6 - 192.168.2.254.

I also tried to change router from DHCP to none DHCP. I deleted all known devices / leases from router and have rebooted proxmox. As soon as I start the VM, proxmox goes blank.

 

[Onslow]

The new VM has 192.168.2.28.
Yes it sound like IP conflict, but no other device on my router has either this IP, nor the IP of the proxmox node nor of my client.
The DHCP range is 192.168.2.6 - 192.168.2.254.

So the PVE host's IP address is in the DHCP range...

Below are some more ideas to check.

Can you ssh from the PVE shell (from its console) to the VM and verify it is this VM really?

Set the IP address of the VM manually to some unused address. Does it help?

If the problem persists, can you disconnect physically the PVE and your workstation from all network devices and connect them directly (using one cable). Of course you have set the IP address of your station manually. Then start the VM. What happens?

If still bad, "disconnect" (virtual) network interface of the VM and start the VM without the network interface. What happens?

 

[Onslow]

@joel-prox You can also read this: https://forum.proxmox.com/threads/f...can-not-load-the-web-gui-in-a-browser.160091/

 

[joel-prox]

I think I solved the problem. For further reference (and people how a really new): The native VLAN on the Port of the node has been Default. Although I used the overwrite function on the specific VM, due to the conectivity loss, that might not have been applied. However, changing this an reinstalling the VM has helped.


Thanks for your help Onslow! Much appreciated!