IPv4 in bridge mode and IPv6 in routed mode for Hetzner dedicated server running Proxmox VE


New Member
May 8, 2023
Dear Proxmox-Community,
I'm running Proxmox VE 8.0.4 on Debian GNU/Linux 12 (Bookworm) using a Hetzner dedicated server. The server comes with one IPv4 address, one MAC, and an IPv6 subnet (/64). I have booked an additional IPv4 and MAC address for a specific VM that needs to be reachable via IPv4 from the internet. Here is what I'm trying to accomplish:
  • The host running Proxmox should be reachable via IPv4 and IPv6
  • I would like to have one bridge (vmbr1) for virtual machines (VMs) using RFC1918 IP addresses and connecting to the internet via NAT
  • I would like to have one segment where VMs get an IPv6 address from my subnet and can communicate with the internet in routed mode to avoid MAC abuse errors (Hetzner allows traffic only from dedicated MAC addresses)
  • The 'proxy-vm' should be accessible from the internet via IPv4 on one interface and via IPv6 on another interface
What I have tried so far

Following you find the configuration of my Proxmox-host. The IP addresses where obfuscated using IPs from RFC5737 and RFC3849.

:~$ cat /etc/network/interfaces
# network interface settings; autogenerated
# Please do NOT modify this file directly, unless you know what
# you're doing.
# If you want to manage parts of the network configuration manually,
# please utilize the 'source' or 'source-directory' directives to do
# so.
# PVE will preserve these directives, but will NOT read its network
# configuration from sourced files, so do not attempt to move any of
# the PVE managed interfaces into external files!

source /etc/network/interfaces.d/*

auto lo
iface lo inet loopback

auto eth0
iface eth0 inet static
    pre-up /sbin/ip addr flush dev eth0 || true

iface eth0 inet6 static
    address 2001:db8:919:1922::1/128
    gateway fe80::1

auto vmbr0
iface vmbr0 inet static
    bridge-ports eth0
    bridge-stp off
    bridge-fd 0

iface vmbr0 inet6 static
    address 2001:db8:919:1922::2/64

auto vmbr1
iface vmbr1 inet static
    bridge-ports none
    bridge-stp off
    bridge-fd 0

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

:~$ cat /etc/network/interfaces.d/vm-routes
iface vmbr0 inet6 static
    up ip -6 route add 2001:db8:919:1922::/64 dev vmbr0

:~$ cat /etc/network/interfaces.d/vmbr0-extra
iface vmbr0 inet static
    hwaddress de:ad:be:ef:73:f1

:~$ ip route
default via dev vmbr0 proto kernel onlink dev vmbr0 proto kernel scope link src dev vmbr0 scope link dev vmbr1 proto kernel scope link src 

:~$ ip -6 route
2a01:4f8:191:2219::/64 dev vmbr0 proto kernel metric 256 pref medium
2a01:4f8:191:2219::/64 dev vmbr0 metric 1024 pref medium
fe80::/64 dev vmbr1 proto kernel metric 256 pref medium
fe80::/64 dev vmbr0 proto kernel metric 256 pref medium

On my VMs I use RHEL. Here is the IP configuration of the proxy-vm that is connected to vmbr0:

ip -br a
  lo        UNKNOWN ::1/128
  ens18        UP 2001:db8:919:1922::3/64 fe80::250:56ff:fe00:XXXX/64
  ip route
  default via dev ens18 proto static metric 100 dev ens18 kernel scope link src metric 100
  ip -6 route
  ::1 dev lo proto kernel metric 256 pref medium
  2001:db8:919:1922::/64 dev ens18 proto kernel metric 100 pref medium
  fe80::/64 dev ens18 proto kernel metric 1024 pref medium
  default via fe80::1 dev ens18 proto static metric 100 pref medium

Other VMs have IPv4 disabled and are using an IPv6 address, e.g. 2001:db8:919:1922::4/64 and IPv6 gateway fe80::1. With this configuration they are able to communicate but cause an MAC abuse error as their MAC is visible on the switch the Proxmox-host is connected to. Currently their virtual NICs are disconnected to avoid the MAC abuse issue.

During my search on the web I read about using a router VM with OPNsense. But I like to avoid using an additional VM for that purpose as I believe it's not necessary.

What do I need help with?
  • Can you check my Proxmox-host and client config for any obvious error that I might have missed?
  • Can someone explain to me how a solution would look like?
  • Is it even possible to have IPv4 in bridged but IPv6 in routed mode?
Your help is much appreciated. If any information is missing from my post I'm happy to provide them when you tell me what is needed.

Best regards,
Last edited:

We have same problem. ipv4 vms are running (bridged config) but we couldn't make ipv6 to work (routed config).

Did you find any solution?


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