服务器集群是实现高性能网络服务的有效结构，而报文转发技术是发挥服务器集群性能的关键。高效的报文转发技术使得集群的调度负载很轻，具有很高的可扩展性。IP隧道技术/直接路由是两种新颖而且高效的报文转发技术。FreeBSD是理想的网络服务器操作系统，但目前基于FreeBSD的集群调度系统均采用网络地址转换技术，系统可扩展性有限。本文讨论了基于FreeBSD操作系统内核，采用IP隧道/直接路由报文转发技术的虚拟服务器(FVS)系统的设计动机及实现，重点探讨了系统的体系结构及实现关键技术。我们基于FreeBSD5.3内核实现了FVS系统，性能测试结果表明，该系统的调度负载很轻，有很好的可扩展性。

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.