In this paper, we design, implement, and evaluate the performance of RackNFV - a high-performance, bandwidth-efficient, and reconfiguration-agile Network Function Virtualization (NFV)/Service Function Chain (SFC) system that operates in a rack. In RackNFV, multiple servers on which Virtual Network Functions (VNFs) are executed and a hardware switch that connects these servers are co-located in a rack. The switch is dynamically partitioned into multiple slice switches that can be flexibly inter-connected to form any desired network topology. The VNF servers can be dynamically connected to the slice switches to form any desired SFC for packet flows. Packets passing through a RackNFV system can be steered through any desired SFC by traversing these slice switches and VNF servers. RackNFV uses the switching capacity of a hardware switch to achieve high-performance and bandwidth-efficient packet forwarding along a chain of VNF servers. By using a novel port-mapping technique, RackNFV can quickly conFigure a new SFC in just 400 milliseconds. Operating in a rack, RackNFV greatly saves the bandwidth in a production network and makes the deployment and maintenance of NFV/SFC faster and easier.