os-net-config/etc/os-net-config/samples/contrail_vrouter_vlan.json

{ "network_config": [
    {
        "type": "contrail_vrouter",
        "name": "vhost0",
        "members": [
            {
                "type": "vlan",
                "vlan_id": 100,
                "device": "em3"
            }
        ],
        "mtu": 1500
    }
  ]
}