As the Software Defined Networking (SDN) paradigm gains momentum, network operators wonder about how to go about replacing their legacy IP routers with SDN-compliant ones. While forklift network upgrades are impractical in operational networks, the promise of SDN is too compelling. Thus, a viable solution is to gradually migrate over time, leading to hybrid OSPF/SDN networks. Although recent studies proposed device architectures, protocols and algorithms required in such hybrid networks, a single routing domain's SDN migration trajectory - as a whole - has hardly been studied. Significance of the sequence in which IP routers are replaced with SDN routers and optimal sequence of router replacements need to be investigated. In this paper, we address these questions based on SDN's traffic engineering (TE) gains and an operator's SDN investment constraints. We propose optimization techniques and heuristics to plan an effective migration schedule in a single routing domain and demonstrate the significance of such a schedule using relevant network management metrics. Our results suggest: (a) the sequence of IP routers migrating to SDN largely determine the resulting TE gains, and, (b) to determine the best migration sequence, novel greedy algorithms perform almost as good as optimization techniques.