This paper presents results from the Cellular IP Project at Columbia University on Internet micromobility. Cellular IP complement Mobile IP with support for fast, seamless and local handoff control, and IP paging. We discuss the design, implementation and evaluation of the Cellular IP protocol using simulation, analysis and experimentation. We report on the ability of Cellular IP to offer seamless mobility for TCP and UDP applications operating in highly mobile environments. We present a comparison of a number of IP micromobility protocols using the Columbia IP Micromobility Software (CIMS) ns‐2 extension that supports separate programming models for Cellular IP, Hawaii and Hierarchical Mobile IP. We discuss simulation results to illustrate the performance of these micromobility protocols. The source code for CIMS and the Cellular IP experimental testbed are freely available from the Web (comet.columbia.edu/cellularip).