Network function virtualization (NFV) introduces great flexibility in designing software-based network appliances to reduce cost and accelerate service deployment for network operators. However, with the fast development of high speed network of 100 GbE and beyond, how to efficiently design virtual network functions (VNF) on commodity servers has become a challenging problem. Although the advances in network hardware and software have facilitated the design of high speed network applications with hardware acceleration and kernel/driver optimization, how to leverage the existing techniques to design optimized high-performance VNFs still remains vague. In this study, we focus on the design and evaluation of four widely used VNFs covering the domains of network switching/routing, access control, measurement and security, by using a multicore platform supported by Intel DPDK fast packet I/O library. We describe the versatile network packet receiving and processing design options available for implementing such a programmable NFV platform for 100 Gbps network speed. With extensive experiments, we evaluate the performance of the each VNF and its design options in terms of packet drop rate, processing time per packet and delay per packet. Based on the evaluation over the collected data, we propose the optimal design with the given hardware resources to sustain the line rate while achieving the highest level of programmability.