in my case, vlan have can't use.
#cat 100.conf
bootdisk: virtio0
cores: 4
ide2: none,media=cdrom
memory: 8192
name: test
net0: virtio=9E:62:1E:83:BF:75,bridge=vmbr4,tag=40
net1: virtio=92:4C:CD:2A:68:0D,bridge=vmbr3
ostype: l26
sockets: 1
virtio0: local:100/vm-100-disk-1.raw
net0 use vlan mode...