VMs lost connection outside LAN after changing subnet


I have originally a LAN network with, with DHCP set to, many devices get a DHCP static IP mapping at 10.0.0.xxx, the rest get a DHCP IP at 10.0.1.xxx.

My VMs in Proxmox all get a static IP mapping starting with

I decided to change all the IPs of my VMs to 10.0.10.xxx. So I changed the LAN interface with After that I changed the DHCP static mappings. I also turned off IPv6 and DHCP6.

After a reboot of everything, VMs all get new IP address because they use DHCP.

The VM can connect to anything in LAN except But all VMs have no internet access. All other devices in LAN with 10.0.0.xxx (DHCP static mapping) and 10.0.1.xxx (DHCP) still work perfectly with internet connection.

For example, I have a VM Unifi Controller at I can open the Web UI via using a PC connected in LAN. The UI opens and the controller sees all my switches.

One switch has IP The VM can ping this IP in terminal and get response.

However, when the VM pings, there is no response. When the VM pings, there is no response. When the VM tries to do apt update, it will fail too because of no internet connection, it doesn’t even resolve the domain name.

Also, a PC connected to LAN can ping my printer in VLAN 10 (, but my VM cannot

A laptop is connected to VLAN 10 (10.10.0.xxx). I cannot open the Web UI of Unifi controller using this laptop. Ping gives “destination host unreachable”.

I set a DHCP static mapping of 10.0.10.xxx to a PC and plug the wired cable. It also gets an IP address just like the VM, and it also experience the same issue.

I must have missed something very simple but I couldn’t figure it out. Feels like something to do with the firewall rules, but I only have default rules in LAN, which are “allow LAN net to anything” for both IPv4 and IPv6.

Does anybody have an idea what probably has gone wrong?

I found it!

I happened to have OpenVPN configured with a very wide IP range and there is IP conflict in this case. After changing the IP range of OpenVPN to another subnet everything works perfectly again.

It’s always handy mapping out your network in Visio or similar.