A major challenge in Internet edge router design is to support both high packet forwarding performance and versatile and efficient packet processing capabilities. The thesis of this research project is that a cluster of PCs connected by a high-speed system area network provides an effective hardware platform for building routers to be used at the edges of the Internet. This paper describes a scalable and extensible edge router architecture called Panama, which supports a novel aggregate route caching scheme, a real-time link scheduling algorithm whose performance overhead is independent of the number of real-time flows, a highly efficient kernel extension mechanism to safely load networking software extensions dynamically, and an integrated resource scheduler which ensures that real-time flows with additional packet processing requirements still meet their end-to-end performance requirements. This paper describes the implementation and evaluation of the first Panama prototype based on a cluster of PCs and Myrinet.