Building extensible routers using network processors

Abstract

This paper describes our effort to build extensible routers using a combination of general-purpose and network processors. We emphasize five overriding challenges that dictate our design decisions: (1) optimal resource allocation; (2) efficient but flexible scheduling of the CPU; (3) maintaining overall router robustness; (4) maximizing router performance; and (5) providing sufficient extensibility to enable the injection of new functionality into the router. We adopt a hierarchical architecture, in which packet flows traverse a range of processing/forwarding paths, thereby partitioning hardware and software in concert. This paper both presents the architecture, and describes our experiences implementing the architecture and addressing the five design challenges in a prototype built from Intel IXP 1200 and a Pentium. 1156 N. SHALABY ET AL.programmed to filter packets, translate addresses, make level-n routing decisions, broker quality of service (QoS) reservations, thin data streams, run proxies, support computationally-weak home electronic devices, serve as the front-end to scalable clusters, support application-specific overlay networks, and even dynamically inject application-specific forwarding code, an effort researched by active networks [1][2][3][4].In response to the pressure of these trends, in order to enable the myriad of services migrating into the network, we extend the notion of a router to include host and server functionality in a flexible way-coining the term extensible router. In addition to supporting extensibility, we have adopted a strategy that employs Commercial off the Shelf (COTS) hardware rather than a custom design-using a hybrid of the newly emerging class of network processors and PCs [5].Network processors are designed to operate under demanding performance requirements and commonly employ parallelism to hide memory latency. They should, therefore, be responsible for forwarding minimal processing packets at line speed, accounting for the bulk of the packets-the data plane. PCs on the other hand, are cheap commodities, with powerful CPUs, which can be employed to process more computationally intensive packets received much less often-the control plane. Nowadays however, the distinction between data and control plane packets is often blurred, with data plane packets requiring more processing, such as the evaluation of firewall rules, or a larger number of control plane packets are received in a single stream, such as the injection of forwarding code into the network (the Active Networks initiative). This fact, coupled with our hybrid hardware, has resulted in a router design with a multi-level processor and execution hierarchy. The hierarchical framework spans all the paths a packet traverses, from the ports, across the processor hierarchy of a network processor, through the kernel space of a general-purpose processor, all the way to the middlebox services and user applications.The main contribution of this paper is to conceptually partition an extensible router into a hierarchy of exe...