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

{ "network_config": [
    {
        "type": "contrail_vrouter",
        "name": "vhost0",
        "members": [
            {
                "type": "interface",
                "name": "em3"
            }
        ],
        "mtu": 1500
    }
  ]
}