Recently many research efforts have been spent on applying Software Defined Networking (SDN) to mobile and wireless networking to make them adapt to the rapid development and popularity of the mobile Internet. SDN offers programmable devices and centralized control which help to realize customizable and adaptive solutions to meet requirements from diversified mobile networks, devices, applications and so forth. This paper focuses on extending SDN paradigm to mobility handling in the Internet which has been little studied, and proposes design, implementation and deployment of a software-defined IP mobility architecture. The paper also demonstrates evaluations and experiments of the proposal based on both the Mininet platform and a cross-domain SDN testbed. Results prove the feasibility, scalability and high adaptability of the proposal.