vlan interfaces not working

[Airw0lf]

Team,

I'm struggling with 2 (out of 4) Ubuntu VM's.
The vlans in these are not working as expected (i.e. eth0.122 and eth0.123).
The output of "ip link" looks fine to me - the same applies for "ip a".

However, pinging the defailt gateway for both vlans is not working.
Everything works fine via eth0.

The relevant output of /var/log/syslog for eth0.122:

Dec 19 09:03:52 proxcum128 systemd[1]: Started ifup for eth0.122.
Dec 19 09:03:52 proxcum128 sh[757]: ifup: waiting for lock on /run/network/ifstate.eth0
Dec 19 09:03:52 proxcum128 systemd-networkd[424]: eth0.122: Link UP
Dec 19 09:03:52 proxcum128 systemd-networkd[424]: eth0.122: Gained carrier
Dec 19 09:03:52 proxcum128 sh[761]: RTNETLINK answers: File exists
Dec 19 09:03:52 proxcum128 sh[718]: ifup: failed to bring up eth0.122
Dec 19 09:03:52 proxcum128 systemd[1]: ifup@eth0.service: Main process exited, code=exited, status=1/FAILURE
Dec 19 09:03:52 proxcum128 systemd[1]: ifup@eth0.service: Failed with result 'exit-code'.
Dec 19 09:03:52 proxcum128 snapd-apparmor[627]: main.go:124: Loading profiles [/var/lib/snapd/apparmor/profiles/snap-confine.snapd.18357 /var/lib/snapd/apparmor/profiles/snap-confine.snapd.>
Dec 19 09:03:52 proxcum128 ifup[772]: RTNETLINK answers: File exists
Dec 19 09:03:52 proxcum128 ifup[626]: ifup: failed to bring up eth0.122
Dec 19 09:03:52 proxcum128 sh[801]: RTNETLINK answers: File exists
Dec 19 09:03:52 proxcum128 sh[757]: ifup: failed to bring up eth0.122
Dec 19 09:03:52 proxcum128 systemd[1]: ifup@eth0.122.service: Main process exited, code=exited, status=1/FAILURE
Dec 19 09:03:52 proxcum128 systemd[1]: ifup@eth0.122.service: Failed with result 'exit-code'.
Dec 19 09:03:52 proxcum128 systemd[1]: networking.service: Main process exited, code=exited, status=1/FAILURE
Dec 19 09:03:52 proxcum128 systemd[1]: networking.service: Failed with result 'exit-code'.
Dec 19 09:03:52 proxcum128 systemd[1]: Failed to start Raise network interfaces.

Proxmox is up-to-date - Ubuntu is not - it is 20.04.3-LTS.
The latter is because the application-vendor (kind-of) insists having this version of Ubuntu.

The qemu, vlan en 802.1q modules are all installed and activated..

Firewall is turned off, for both Proxmox and VM.
In addition, vmbr0 is vlan aware for id 2-4094

Initially, everything was configured in Netplan - which is now removed and replaced with ifupdown.
This didn't help either.

Any suggestion how to troubleshoot this?

 

[jsterr]

How does the vm config look like? qm config VMID Why are you not giving the vm multiple adapters with each adapter having its own vlan set in the vm-config?