Thanks. I've set the limit in the VM config against the 'net0' device:
balloon: 512
boot: cdn
bootdisk: virtio0
cores: 2
ide2: none,media=cdrom
memory: 2048
name: XXXXXX
net0: virtio=E6:2A:96:74:9E:75,bridge=vmbr0,rate=4,tag=730
onboot: 1
ostype: l26
smbios1...