A method and apparatus are provided for determining a service interruption time measurement including routing protocol convergence time and Forwarding Information Base (FIB) insertion time, between network devices A and B in a network which has a routing protocol. A plurality of probe packets are then sent from the device A to the device B, each probe packet comprising a source address corresponding to the device A. A network route to the device A for the source IP address used by the probe packets is unknown to the network. A sequence number and sending time is typically assigned to each probe packet being sent. At a predetermined time, a route to the source address of the device A is injected into the routing protocol. Upon return to the device A of a first of the probe packets, an arrival time to is detected and an upper bound and a lower bound of the service interruption time measurement is calculated.