This article presents an overview of a set of IP-based mobility protocols mobile IP, HAWAII, cellular IP, hierarchical MIP, TeIeMIP, dynamic mobility agent, and terminal independent MIP - that will play an important role in the forthcoming convergence of IP and legacy wireless networks. A comparative analysis with respect to system parameters such as location update, handoff latency and signaling overhead exposes their ability in managing micro/macro/global-level mobility. We use this observation to relate their features against a number of key design issues identified for seamless IP-based mobility as envisioned for future 4G networks.