A warning about VLANs in Proxmox or general Linux networking

A heads-up for those working with Proxmox or dealing with ifupdown networking in general.

Keyword bait:

• my Proxmox server sees the network but none of its VMs do
• when trying to put my Proxmox server on a VLAN it drops off the network

If you are trying to set up VLAN handling on your server, be extremely aware of which VLANs are tagged and which are native on your upstream switch port. If you have a native VLAN specified, do not list it in the VLAN list.

For example, suppose you have VLANs 10, 20, and 30, and suppose that your upstream switch port has VLAN 10 as native, and has VLANs 20 and 30 tagged. One way to do this in your config is to say:

auto vmbr0
iface vmbr0 inet static
        address 192.168.10.50 # an address on VLAN 10
        gateway 192.168.10.1
        bridge-ports en0
        bridge-stp off
        bridge-fd 0
        bridge-vlan-aware yes
        bridge-vids 20 30 # do not have 10 here!!!

And then, in the VMs, if you want it to be on VLAN 20 or 30 explicitly specify that, but if you want it to be on VLAN 10, leave the VLAN field blank, and rely on the upstream switch to handle putting the untagged traffic onto VLAN 10.

The other way of handling this is to set your switch to tag every VLAN, and have no native VLAN on the port. Then, your configuration will be:

auto vmbr0
iface vmbr0 inet manual
        bridge-ports en0
        bridge-stp off
        bridge-fd 0
        bridge-vlan-aware yes
        bridge-vids 10 20 30 # now you have 10 here because it’s tagged upstream

auto vmbr0.10
iface vmbr0.10 inet static
        address 192.168.10.50
        gateway 192.168.10.1

And then, in your VMs, you explicitly tag every VLAN that you use, and you don’t have to worry about which are native upstream on your switch because none are.

Good luck!