Server cluster is an efficient architecture for providing high performance networkservices, and the packet forwarding technique plays an important role in exploiting theperformance of server clusters. Efficient packet forwarding techniques incur low schedulingoverhead, and have high scalability. IP Tunneling/Direct Routing are novel and efficientpacket forwarding techniques. FreeBSD is an ideal network server operating system. However,the packet forwarding technique adopted in the current FreeBSD based server cluster schedulersare all network address translation, which has a limited scalability. This paper describes themotivation, design, and implementation of FVS (FreeBSD Virtual Server), which works inside theFreeBSD kernel and adopts the IP Tunneling/Direct Routing techniques. The discussion focuseson the system architecture and the key implementation techniques. We have implemented FVS on

the FreeBSD5.3 release, and the experimental results show that the system incurs very low

overload, thus achieves high scalability.