VM Can't connect network when their bridge is on a specific NIC


Oct 27, 2015
Hello Everyone, I need your help

I'm a Proxmox user and enthousiast. I've recently changed one of the 2 Physical server (node) of my office and I've spent hours trying to understand why my vms couldn't get connected to the network despite I've done exactly like all the other time I've installed proxmox in the past on other machines.

Problem : When my VM has it Virtual LAN card on a VMBR that is on my QNAP Network card, the VM can't connect the physical LAN and LAN can't connect the VM, BUT the LAN can connect the proxmox which is connect to this VMBR. The Proxmox can connect the VM also. When I change the VMBR link to another Network Card, everything work correctly.

A resume for the Hardware :
The server has 4 Network cards :
On Motherboard (MSI MAG B550 TOMAHAWK) :
  • Realtek Semiconductor Co., Ltd. Device 8125 (rev 04)
    • Identify : enp42s0
    • Bandwith : 2.5G
    • driver declared by system : r8169, r8125 (had to install them manually)
    • Use for : LAN
  • RTL8111/8168/8411 PCI Express Gigabit Ethernet Controller
    • Identify : enp40s0
    • Bandwith : 1G
    • Driver declared by system : r8169
    • use for : WAN connection (my pfsense is a VM)
On a QNAP PCIe Card (QNAP QXG-2G2T-I225) (The Cards where the problem occurs)
  • Ethernet controller: Intel Corporation Device 15f2 (rev 02)
    • identify : enp35s0
    • Bandwith : 2.5G
    • Driver : igc
    • Use for NAS network
  • Ethernet controller: Intel Corporation Device 15f2 (rev 02)
    • identify : enp38s0
    • Bandwith : 2.5G
    • Driver : igc
    • Use for LAN bis and Management network
Here is my /etc/network/interfaces :
auto lo
iface lo inet loopback

iface enp40s0 inet manual
#Wan Interface

iface enp35s0 inet manual
        mtu 9000
#NAS Interface

iface enp38s0 inet manual
#LAN Interface

iface enp42s0 inet manual
#Non working Management Interface

auto vmbr0
iface vmbr0 inet static
#       address
#       gateway
        bridge-ports enp42s0
        bridge-stp off
        bridge-fd 0
#Lan Network

auto vmbr1
iface vmbr1 inet static
        bridge-ports enp35s0
        bridge-stp off
        bridge-fd 0
        mtu 9000
        pre-up ( ifconfig enp35s0 mtu 9000 )
#NAS Network

auto vmbr2
iface vmbr2 inet manual
        bridge-ports enp42s0.6
        bridge-stp off
        bridge-fd 0
#DMZ Network

auto vmbr3
iface vmbr3 inet static
        bridge-ports enp42s0.7
        bridge-stp off
        bridge-fd 0
#DCLIC Network

auto vmbr4
iface vmbr4 inet static
        bridge-ports enp42s0.8
        bridge-stp off
        bridge-fd 0
#SASERP Network

auto vmbr5
iface vmbr5 inet manual
        bridge-ports enp40s0
        bridge-stp off
        bridge-fd 0
#Wan Network

auto vmbr6
iface vmbr6 inet manual
        bridge-ports none
        bridge-stp off
        bridge-fd 0
#Guest Network

auto vmbr7
iface vmbr7 inet manual
        bridge-ports enp38s0
        bridge-stp off
        bridge-fd 0
#Management Network

here is my Versions pveversion :
pve-manager/6.2-15/48bd51b6 (running kernel: 5.4.65-1-pve)

I hope this will help you to help me. I might have done something wrong or have done something necessary but I really have the impression not to have differently than usually and thing that my config is not so special. I would really appreciate your help please.
Kind regards,


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