Virtual Routers: A Tool for Networking Research and Education Florian Baumgartner, Torsten Braun, Eveline Kurt, Attila Weyland Universität Bern, Neubrückstrasse 10, 3012 Bern Phone/Fax: +41 31 631 4994/3261 [baumgart|braun|kurt|weyland]@iam.unibe.ch] ABSTRACT Virtual routers are software entities, i.e. user space processes, emulating IP routers on one or several (Linux) computers. Virtual routers can be used for both networking research and education. In contrast to simulation, virtual routers process packets in real-time and the virtual router code is similar to code in real routers. In the case of research, larger network test-beds can be built using a relatively small number of computers. New functionalities such as new queuing mechanisms are supported by a modular software architecture and can be tested in a rather safe environment compared to kernel space implementations. Virtual routers can also be used as a tool aiming to allow students to perform virtual experiments within a computer networks course. Students can create and experiment with arbitrary virtual IP network topologies. The web-based user interface allows students to interact remotely with the emulated routers, but simultaneously it is very similar to commonly available configuration interfaces of network devices in reality. This enables students to configure routers like in the real world but also to experiment in a much more robust and safe environment. Categories and Subject Descriptors C.2.6 Internetworking General Terms Management, Measurement, Performance, Design, Experimentation. Keywords Network Emulation, Performance Evaluation, Networking, Distance Learning 1. Introduction The strengths and drawbacks of network simulators, like the ns network simulator [6], lie in the use of a mathematical model to simulate a network, a node or a link between two nodes. Since there is no relationship between real time and the time ns uses internally, ns can be used to run huge simulations with thousands of nodes and links. The simulation simply will last longer, but is nevertheless mathematically correct. The use of such a model includes a rather abstract view of a network consisting of nodes and links. These properties are sufficient to simulate the traffic flow of thousands of nodes within a huge network. For the development of new network protocols, however, protocol implementations should be closer to real system environments and real-time packet processing is desirable in order to support a larger variety of performance evaluations. In particular, it would be advantageous if new functionalities can be tested in real environments with typical applications and network scenarios. Another requirement appears for networking education. Students should be able to perform practical networking experiments, but at least for early steps safe and robust laboratory environments are desirable. Both of these application scenarios, i.e. research and education, are supported by a concept called virtual routers. Virtual routers emulate IP routers and can support flexibility and robustness by a modular software architecture and user space processing. We propose to use emulated routers not only for research and development, but also for distance learning allowing students to perform computer network experiments remotely and within a safe environment. This allows students to prepare themselves for later experiments that are performed remotely with real network devices [3]. Remote experiments are very popular in various areas such as nano-science [7], engineering [8][9], computer networks [10] etc. This paper discusses related work in Section 2. It then introduces the implementation architecture of virtual routers in Section 3. Section 4 evaluates the performance of virtual routers using several different scenarios. Section 5 shows how virtual routers can be used for networking research and Section 6 shows how students can use virtual routers in a web-based networking course. Section 7 concludes the paper. 2. Related Work The emulation of network devices or routers is not new. Emulab [17] is an ongoing project providing a large test-bed for the emulation of networks. The test-bed can be accessed remotely and provides mechanisms to use ns2 scripts [6] for the configuration of the test network. The Emulab approach is very flexible and powerful, but requires a large set of computers and network devices. Similar to the Emulab approach, several other approaches, even usually on a smaller scale, use single computers to emulate specific routers [4][5][16]. The Click modular router is a highly modular and well performing software router implementation, which allows the emulation of a very flexible, easy to configure router on a single computer. ACM SIGCOMM Computer Communications Review Volume 33, Number 3: July 2003127To reduce the hardware resource consumption, some of these approaches support the partitioning of the hardware into multiple logically completely independent computers using virtual machines (e.g. VMware), allowing the execution of multiple routers on a single computer. Another approach is to virtualize a host’s process network and file-system namespace [22]. In contrast virtual routers do not require partitioning the hardware platform, but are designed to be run in parallel in user space and to use high level communication channels for interconnections. While this requires a modification of applications, it also allows providing simpler interfaces. There are other more specific approaches to emulate the typical behavior of a special network device (e.g. a WAN Router) or a specific link. NistNet [21] uses Linux kernel modules to emulate the behavior of a specific link and allows the emulation of WANs within a standard laboratory LAN. Another approach to reduce the amount of required equipment has been proposed by Wang et al. [18]. They use an address mapping scheme in the kernel to route packets multiple times through the same host. This allows studying the impact of multiple hops on a single computer. Also ns2 [6] supports the interconnection of real network devices with simulated environments and allows to route packets through a simulated network. However, since it is a simulator, ns2 has a completely different architecture and completely different interfaces than normal IP routers. Especially the completely different user interface is a drawback in the context of a course teaching the configuration of
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