Abstract-Most of the previous works on evaluating IPv6 have focused on network throughput and packet delay performance studies. A thorough literature review reveals that a very limited research have been conducted on evaluating IPv6 using quality of service (QoS) parameters and modern operating systems (OSs). The objective of this paper is to evaluate the UDP performance of IPv6 in a peer-to-peer Gigabit Ethernet network using the latest four different MS Windows and Linux-based client and server OSs. The QoS metrics such as throughput, end-to-end delay, jitter, and CPU utilization are measured empirically to determine which OSs provide the best bandwidth performance over IPv6 networks. The impact of packet length on system performance is also reported. Results show that for IPv6 Linux network using Ubuntu 10.04 performs significantly better than Windows 7.