In　today＇s　networks,　load　balancing　and　priority　queues　in　switches　are　used　to　support　various　quality-of-service　(QoS)　features　and　provide　preferential　treatment　to　certain　types　of　traffic.　Traditionally,　network　operators　use　＇traceroute＇　and　＇ping＇　to　troubleshoot　load　balancing　and　QoS　problems.　However,　these　tools　are　not　supported　by　the　common　OpenFlow-based　switches　in　software-defined　networking　(SDN).　In　addition,　traceroute　and　ping　have　potential　problems.　Because　load　balancing　mechanisms　balance　flows　to　different　paths,　it　is　impossible　for　these　tools　to　send　a　single　type　of　probe　packet　to　find　the　forwarding　paths　of　flows　and　measure　latencies.　Therefore,　tracing　flows＇　real　forwarding　paths　is　needed　before　measuring　their　latencies,　and　path　tracing　and　latency　measurement　should　be　jointly　considered.　To　this　end,　FlowTrace　is　proposed　to　find　arbitrary　flow　paths　and　measure　flow　latencies　in　OpenFlow　networks.　FlowTrace　collects　all　flow　entries　and　calculates　flow　paths　according　to　the　collected　flow　entries.　However,　polling　flow　entries　from　switches　will　induce　high　overhead　in　the　control　plane　of　SDN.　Therefore,　a　passive　flow　table　collecting　method　with　zero　control　plane　overhead　is　proposed　to　address　this　problem.　After　finding　flows＇　real　forwarding　paths,　FlowTrace　uses　a　new　measurement　method　to　measure　the　latencies　of　different　flows.　Results　of　experiments　conducted　in　Mininet　indicate　that　FlowTrace　can　correctly　find　flow　paths　and　accurately　measure　the　latencies　of　flows　in　different　priority　classes.