Software-defined networking (SDN) aims to provide open interfaces, such as OpenFlow protocol, that enable programmable flow-based network management. Meanwhile, OpenFlow-enabled switches provide rich statistical information for specific flows, tables, and ports which facilitates various network management tasks. However, current traffic monitoring techniques collecting statistics from existing flow entries do not provide the flexibility of querying path-specific flow statistics at any aggregation levels. In this paper, we proposes PathMon which encodes flow and path information as tags to provide that flexibility and corresponding link-to-link correlations for further anomaly detection or traffic engineering tasks. Our implementation runs on commodity switches which are compliant to OpenFlow 1.3 specification and requires only a few monitoring entries for each switch along monitored paths and un-tag entries for each edge switch.