[SOLVED] Routing problem in Proxmox VMs to OPNSense

a2c

New Member
Nov 7, 2025
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Hello, I am new to the forum with very little experience on Proxmox. This is also my first request for help. I have searched, consulted numerous subjects here and I admit either to being totally useless or totally ignorant or not knowing how to read the present subjects correctly, but today I encountered a difficulty which can seem, I am sure, very banal and certainly discussed dozens of times.

My configuration is as follows:
- Server on a Minis Forum BD795S7 with 64GB of memory, 1 SSD drive of 1TB and 1 of 2TB;​
- Proxmox version 9.0.11​
- 1 physical network card at 1GB (enp4s0)​
- 1 USB network card at 2.5GB (enusb0)​
- VM OPNSense in version 25.7.5​
- VM Debian 13 (Trixie)​

Proxmox is connected to the classic local network behind the Orange box (epn4s0)
A station is connected to a second network which I call "Private LAN" (enusb0)

I would like to carry out the following scenario which seems to be simple but which I cannot resolve:
All VMs in Proxmox and all stations in the "Private LAN" will only be able to access the Internet if the OPNSense VM is running.
Which of course means that if the OPNSense VM is shut down, no more VM or workstation will be able to go on the Internet.

Here's what works at the moment:
- All VMs can go on the Internet​
- All stations on the "Private LAN" can only go to the Internet if i change the "bridge-ports none" parameter in vmbr2 to "bridge-ports enusb0"​
- If OPNSense is stopped, the VMs and "Private LAN" can still go on the Internet​

I've been trying different configurations in the /etc/network/interfaces file for hours and days and I can't achieve my goal.
I would appreciate a helping hand or a lead to understand what my errors are, as I am sure there must be several or even it may not be possible to achieve my wish.
For your help, here is my current etc/network/interfaces file :

Bash:
auto lo
iface lo inet loopback

auto enp4s0
iface enp4s0 inet manual
        post-up ip route add 192.168.10.0/24 via 10.120.0.1

auto enusb0
iface enusb0 inet manual

auto vmbr0
iface vmbr0 inet static
        address 192.168.1.115/24
        gateway 192.168.1.1
        bridge-ports enp4s0
        bridge-stp off
        bridge-fd 0
#WAN Proxmox

auto vmbr1
iface vmbr1 inet static
        address 10.120.0.1/30
        bridge-ports none
        bridge-stp off
        bridge-fd 0
#WAN OPNSense

auto vmbr2
iface vmbr2 inet static
        address 192.168.10.254/24
        bridge-ports enusb0
        bridge-stp off
        bridge-fd 0

        post-up echo 1 > /proc/sys/net/ipv4/ip_forward
        post-up iptables -t nat -A POSTROUTING -s '192.168.10.0/24' -o vmbr0 -j MASQUERADE
        post-down iptables -t nat -D POSTROUTING -s '192.168.10.0/24' -o vmbr0 -j MASQUERADE
#LAN OPNSense

source /etc/network/interfaces.d/*
 
As I had a lot of help from the community I found the errors on my own. In fact there were 3 in the /etc/network/interfaces configuration file that I showed in the previous post.

I thought that OPNSense was capable of managing routes when told which way to go, I realized that this is not always the case.

In any case, everything works now and I'm marking the post as resolved.