We present the design and the implementation of an open shortest path first (OSPF) monitoring service hooked up to a managed IP network, enabling the administrator to be aware of the paths currently taken by IP packets throughout the OSPF domain. Such a service represent an advance over tools available today that offer off-line emulations of routing protocols, or that track network routing behavior in a local, semi-static manner. The proposed routing monitoring service has applications to network management functions such as QoS service fulfilment, performance analysis and SLA verification.