The internal processing time in OSPF implementation impacts the speed of routing updates propagating, network convergence time and OSPF scalability in a network. The scalability issue of OSPFTE is critical, because available bandwidth changes on a link will generate updates packets frequently and cost more CPU power for routers to receive and process those updates. In this paper, we study OSPFTE scalability in a single area and identify scalability related performance parameters by white-box measurements on Zebra implementation. We draw conclusions on how to enhance OSPF implementations according to the measurement results. Compared with black-box OSPF measurement, our experience provides reference for those equipment vendors and network designers to figure out key parameters that are related to implementation performance, so that they can be aware of scalability limitation, and improve their implementations.