Clustered server architecture has been employed for many years on the Internet as a way to increase performance, reliability and scalability in the presence of the Internet's explosive growth. Routing mechanism for mapping requests to individual servers within cluster is at the heart of any server clustering techniques. In this paper, we first analyze the deficiencies of existing request routing approaches. Based on these observations, we argue that the request routing mechanism in the cluster-based server should factor in the content of a request in making decisions. Thus, we design and implement a new mechanism to efficiently support content-based routing in the Web server clusters. Performance evaluation on a prototype implementation demonstrates substantial performance improvements over contemporary routing scheme that use weighted round-robin to distribute requests. The proposed mechanism can enable many new capabilities in cluster-based server, such as sophisticated load balancing, differentiated service, special content deployment, session integrity, etc.