[SOLVED] Proxmox bridged networking on Hetzner root server difficulties

[Gregyski]

I have been trying to setup proxmox on a Hetzner dedicated root server in a bridged configuration for the past day. Right now I only have the 1 IP. I intend to ultimately run an opnsense VM and NAT that IP for a couple VMs and eventually purchase a couple more IPs for some other VMs, but don't see the point until I resolve the current issues. I've been able to install proxmox successfully, but have not been able to get networking operational. I've tried a dozen variations of settings including (obfuscation note: assigned IP is x.x.x.x, gateway IP is y.y.y.y):

# https://community.hetzner.com/tutorials/install-and-configure-proxmox_ve#bridged-setup
auto lo
iface lo inet loopback

auto enp0s31f6
iface enp0s31f6 inet manual

auto vmbr0
iface vmbr0 inet static
        address x.x.x.x/32    # Main IP - also tried /27
        gateway y.y.y.y       # Gateway
        bridge-ports enp0s31f6
        bridge-stp off
        bridge-fd 0

and

# https://cyanlabs.net/tutorials/install-proxmox-on-a-hetzner-dedicated-server-with-1-ip-using-sdn-and-without-kvm-using-qemu/
auto lo
iface lo inet loopback

iface enp0s31f6 inet manual

auto vmbr0
iface vmbr0 inet static
        address x.x.x.x/27    # Main IP - also tried /32
        gateway y.y.y.y       # Gateway
        bridge_ports enp0s31f6
        bridge_stp off
        bridge_fd 0

and a number of other suggestions from reddit, this forum and elsewhere. At one point I was able to get the proxmox GUI accessible externally by using eno1 instead of enp0s31f6 but could not connect out from the proxmox server at all (could ping itself, but not even the gateway). Since then, I haven't even been able to reproduce that limited success. I've verified Hetzner's firewall is allowing all out and allowing all in from the IP I'm working from. Substituting eth0 for enp0s31f6 doesn't work either.

ip addr for the relevant interface from Hetzner Rescue reads as follows:

2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
    link/ether zz:zz:zz:zz:zz:zz brd ff:ff:ff:ff:ff:ff
    altname eno1
    altname enp0s31f6
    inet x.x.x.x/27 scope global eth0
       valid_lft forever preferred_lft forever

I'd greatly appreciate assistance in getting this working. Thanks!

Edit: By pinning the interface MAC to eth0 and then using eth0 for the bridge interface and otherwise matching the second /etc/network/interface above, I'm back at being able to access the Proxmox GUI. But Proxmox itself cannot ping or connect outside of itself. I'll continue to diagnose.

Edit 2: The second problem turned out to be my misconfiguration of the Hetzner firewall. I was blocking incoming DNS... That said, the initial problem was still very real which is solved by pinning the interface to the MAC. This was 100% necessary for me despite not being in any of the Hetzner tutorials. I even did a completely fresh installation process using a different Hetzner tutorial (https://community.hetzner.com/tutorials/proxmox-docker-zfs) and still had to pin the interface by creating /etc/systemd/network/10-eno1.link:

[Match]
MACAddress=zz:zz:zz:zz:zz:zz
Type=ether

[Link]
Name=eno1