opnet实验指导

OPNET IT GURU: A TOOL FOR NETWORKING EDUCATION MSCIT Practicum Paper REGIS UNIVERSITY BY Ranjan Kaparti Professor Dan Likarish 2 TABLE OF CONTENTS Chapter 1: Introduction Page 3 Chapter 2: Solutions Page 6 Chapter 3: OPNET IT Guru Overview Page 9 Chapter 4: OPNET IT Guru for Education Page 17 Chapter 5: Multimedia Quickstart and Labs Page 21 References Page 41 3 Chapter 1: Introduction: The Problem Computer networks are ubiquitous and such a state of affairs creates demand for qualified personnel who can work with networks. Unsurprisingly many institutions of learning (high- school and higher learning) are teaching the relevant set of networking technologies. Many are interested in creating new programs and curricula with networking content. The question arises as to how best to teach this material. Michael Dixon, Tanya McGill, and Johann Karlsson point out that many of the relevant concepts are difficult to really grasp in a purely theoretical way. Lectures alone do not accomplish the trick. And practical assignments - labs - must move beyond mere programming assignments. Though writing say, a custom communications protocol, is a good exercise, it falls short if the goal is to teach the big picture of network communications and associated high-level decision making and analysis. (Dixon, McGill and Karlsson 71) The nature of the technology itself is such that it is difficult to get “hands on” with it from the point of view making the technology available for classroom use. There is the issue of expense. Many high schools for instance may not have the resources to build an appropriate lab with all relevant hardware and software. Furthermore real world networks may span not 4 merely a lab or two but rather entire buildings or even multiple global locations. Noel Davis, Scot Ransbottom and Drew Hamilton point out that: Most networks are built to accommodate the needs of a single organization or group. Internetworking is a technology that accommodates multiple, diverse, underlying hardware by providing the means of interconnecting heterogeneous networks. Comparatively few individuals, academic institutions or corporations have networks exclusively dedicated for student use and experimentation. Prudent administrators limit student or general user access to operational networks. (Davis, Ransbottom and Hamilton 104) Davis et al make some good points here. Even if there is a network designated for student use it is rare that the network’s sole purpose is to support the networking curriculum. Students may gain valuable experience managing a network which is in deployment (for general uses); however such experience has limitations. For instance suppose a school decides to run the Windows family of servers on their networks and the school designates a lab for networking students’ use. Students may learn a lot about Windows servers and associated technologies but they will not obtain hands on training with Linux based technologies. Even if one sets aside the worry about not being able to learn the relevant range of technologies, students will likely not be allowed to change settings and reconfigure things to any significant extent in the Windows based network. The bottom line seems to be that networking curricula face the following dilemma: on the one hand it is expensive to set up a networking lab and on the other, even if one makes that 5 investment, such labs have significant limitations from the point of view of pedagogy. One cannot hope to cover the diversity of technologies and configurations and furthermore large scale networks cannot be built specifically for student use – the costs are surely too prohibitive. This problem of making available appropriate hands on computer networking training is even more acute if one considers distance education. In distance education (whether synchronous online, asynchronous online, video based) students are in disparate locations. It would be impossible to collect them together for the sake of hands-on training – unless one mandates that for brief periods of time – in which case it no longer would be really purely distance learning. Indeed according to Brian Cameron and K. Wijekumar: Computer networking, as defined as the interconnection of computers and computing equipment using either wires or radio waves over small or large geographic areas (White, 1994), has long been regarded as one of the more difficult technology- related subjects to teach. Historically, this type of course was thought to require much hands-on interaction with the instructor and was not viewed as a good candidate for an online course. (Cameron and Wijekumar, 117) It would be hard to imagine serious educational institutions creating mini networking labs with actual hardware in every distance learning student home or workplace. The costs, even if partially to be passed on to the students, are simply too high. 6 Chapter 2: Solutions Even though the picture prima facie appears bleak, there are some viable solutions that would address not only the needs of traditional but also those of non-traditional (distance) networking students. The main solution of interest here is network modeling and simulation software. In particular OPNET IT Guru is going to be the focus. Appropriate network modeling and simulation software could be used to model networks down and up to whatever scale or detail that is necessary. Students learn by creating virtual networks and devices of all kinds and are not limited by network hardware availability concerns. There is the prospect that distance students can participate fully – all it would take is student access to a workstation to run the software. The student’s home computer itself would likely fit the bill. Indeed studies have already been done that show significantly improved learning outcomes in networking technology distance students who used network modeling and simulation software and those distance students who did not. Cameron and Wijekumar claim that network simulation software increases student motivation in online courses. One of the biggest problems in distance education (according to them) is lack of sustained student motivation and involvement. Network simulation software 7 gives students something tangible to do – a feeling of having accomplishing something real and hands on and thus lessens drop out rates. (Cameron and Wijekumar, 116f) Cameron and Wijekumar actually conducted a study with an online networking course for undergraduates (Cameron and Wijekumar, 118). One course used “static” network design package - Microsoft Visio - for design assignments while the other course used network simulation and modeling software for all their work. It was not OPNET IT Guru but rather one made by NetCracker Corporation. Nonetheless NetCracker’s software is dynamic as well – permitting a range of modeling, design and simulation functionality (LAN, MAN, WAN). It was found that students with NetCracker software had a lower drop out rate, and rated their learning to be much higher. They spent more time on their assignments and explored “what if” scenarios. The ones with Microsoft Visio felt that they did not quite know if their network designs really worked or not before submitting them to the instructor. Cameron and Wijekumar further point to a number of studies which collectively suggest the following good things about simulation and modeling as a general pedagogical technique: (a) “Simulations enable knowledge application through multidimensional problem solving.” (Cameron and Wijekumar, 119) 8 (b) “Simulations have been shown to improve knowledge transfer(Cameron and Wijekumar, 119) (c) “Simulations have been shown to increase understanding of abstract concepts.” (Cameron and Wijekumar, 119) (d) “Simulations and modeling can help instructors target students at multiple levels of learning.” (Cameron and Wijekumar, 119) (e) “Simulations have the potential to improve students’ abilities with complex and evolving problem solving situations.” (Cameron and Wijekumar, 119) It seems therefore to be almost a “no-brainer” to incorporate network simulation and modeling software into the curriculum. The advantages in terms of cost, student involvement and learning outcomes, utility in distance learning, the ability to give practical experiences about technologies of a wide range and/or that are simply too expensive are so impressive and great that it makes very little sense to reject this solution. In the market there appear to be two major options for networking and simulation software. Boson’s NetSim and OPNET’s IT Guru are mentioned widely in the literature. The latter appears to be more widely adopted in academy. The former seems to target the Cisco’s line of networking examination and prep markets and not necessarily networking in general (Boson Corporation, “Boson NetSim: Education by Simulation”). In contrast IT Guru is comprehensive and technology neutral in its capabilities and versatility. However that fact by itself ought not to count against NetSim. It may be that both pieces of software have worthwhile roles to play in the curriculum. For the sake of focus OPNET’s IT Guru will be pursued in depth here. 9 Chapter 3: OPNET IT Guru: Overview IT Guru enables one to create a virtual network consisting of relevant hardware, protocols, and application software (OPNET Corporation, Slide 2 of “IT Guru QuickStart”, PowerPoint Presentation, 2004). This network is a purely software entity that can run on an individual workstation. Routers, switches, web servers – almost anything found in real networks – can be duplicated in an IT Guru virtual network. It can be scaled from just a network of two workstations to one representing tens of thousands running in a WAN. Once a virtual network is created it can be manipulated in various ways – for instance routers can be added or subtracted, protocols switched around or altered, web servers added or discarded – any permutation imaginable. The effects of various alterations and diverse configurations can then be usefully and quantifiably examined and analyzed. Importantly IT Guru allows one to study and gather useful statistics about a virtual network built from it. IT Guru permits not only the building of a virtual network in software but also provides tools for dynamically investigating the thus engendered network. (OPNET Corporation, Slide 17 of “IT Guru QuickStart”, PowerPoint Presentation, 2004). 10 The following high level architectural rendering of IT Guru is an ideal place to get started. It shows IT Guru and its major modules: Source: OPNET Corporation, Slide 377 of “IT Guru QuickStart”, PowerPoint Presentation, 2004 The virtual network environment represents a network. It can have a slew of components in every salient category. Opnet defines a topology as a “collection of links, nodes and configuration.” (OPNET Corporation, Slide 203 of “IT Guru QuickStart”, PowerPoint Presentation, 2004) By “nodes” Opnet means to include networking hardware of all kinds (routers, workstations, switches, hubs etc). By “links” the underlying connectivity technology (Ethernet, ATM, etc) and relevant characteristics (latency, bandwidth) are meant. In IT Guru Workflow – Inputs and Outputs Virtual Network Environment Traffic, Topology, and Configuration Application Trace Flow Analysis: Visualize and study steady-state data flow, capacity planning, failure analysis – extensive reporting NetDoctor: Operational configuration validation – protocol-specific and policy-based DES: Simulates precise protocol effects for capacity planning, tuning protocol behavior, response time engineering, technology migration, QoS, etc. ACE: Application performance troubleshooting: visualize performance, diagnose problems, explore solutions MVI, VNES, GUI Sniffer, OPNET Application Capture Agent, etc. Steady-state Throughput/Util; 100+ Reports; Path/Failure Flow Analysis Configuration validation NetDoctor Graphs, web reports, charts, for all time-varying network performance metrics (e.g., app response time, queue depths, ti t l DES Application Visualization, Diagnosis, Analysis, Protocol ACE 11 “configuration” things like routing protocols, addressing, whether VPN, are included. Some combination of nodes, links, and configuration makes up a VNE. (OPNET Corporation, Slide 203 of “IT Guru QuickStart”, PowerPoint Presentation, 2004) As the diagram shows there are several different ways of creating an OPNET virtual network environment (VNE). The most straightforward is by using OPNET’s GUI interface for that purpose. One can select from a list of choices for all aspects of a network. The general procedure is to select appropriate hardware elements such as workstations, servers, routers, switches, hubs, then connect them together according to the desired topology. OPNET provides models of the major popular brands of network communication hardware – Cisco for instance is well represented with its family of routers and switches available in the relevant OPNET IT Guru menus. (OPNET Corporation, Slide 205, Slides 221-223 of “IT Guru QuickStart”, PowerPoint Presentation, 2004) The GUI method works well in many contexts surely but it can be tedious if the network being modeled is elaborate and complex. OPNET has made it possible to automate VNE creation via the VNE Server technology. The VNE Server works in conjunction with OPNET VNE clients to gather user specified network data. It then has the ability to feed that data into IT Guru, producing a virtual representation of the network. Clearly this is a highly 12 powerful method of engendering a VNE. It has the added advantage of sidestepping user errors that are possible in a manual VNE creation process. Actually VNE server is powerful enough to process network topology data from not only OPNET clients but also industry standard network mapping and monitoring agents. For instance VNE server can interface with HP Openview NNM, Cisco Netflow Collector in addition to having the capacity to gather information directly from various Cisco, Juniper and Nortel switches and routers. It can also read from SNMP MIBs and in the worst-case scenario perhaps ASCII files containing sundry topology related information. (OPNET Corporation, Slide 207 of “IT Guru QuickStart”, PowerPoint Presentation, 2004) IT Guru can also utilize network device configuration file information to create a VNE. Routers, for instance, have associated configuration files that contain commands to the router OS. Such files can be fed into IT Guru and IT Guru can in turn generate topology information from them. The restriction is that only Cisco and Juniper devices are currently supported. (OPNET Corporation, Slide 208 of “IT Guru QuickStart”, PowerPoint Presentation, 2004) Opnet has devoted an entire specialized module called Application Characterization Environment (ACE) for modeling and analyzing the 13 behavior of programs that reside above and are primarily users of the network. In other words, these are above the topology layer – they use network services but are not themselves strictly speaking, part of the topology. Consider a web browser, or a video conferencing client. Or a database query tool that talks to a database over the network. Any and all such applications can be modeled in IT Guru – one can make custom virtual representations of such program and populate them inside a VNE. Not only can IT Guru simulate network topology in the VNE but also any high level application that runs on the network. One must hasten to clarify that it is not that the entire application’s logic and functionality will be duplicated inside the VNE. Rather ACE (using appropriate Opnet agents) captures an application’s communications and interactions with the underlying network topology. This sort of snapshot of an application’s network communications is called an application’s “trace”. As an illustration of how ACE could be used, suppose there is a new web application that remote users access on a DSL connection. However they are experiencing more than expected latency and delay. Suppose that ACE traces have been captured both at the client and server. Now ACE, working in conjunction with IT Guru, has the ability to simulate and analyze the entire client server interaction here. The transactions between client and server here can be simulated inside the appropriately constructed VNE. ACE and IT Guru gives one the ability to 14 conduct detailed studies that would hopefully pin-point what the trouble may be (or at the very least rule out problem spots). For instance, it may be that the server is behaving correctly but the client is firing requests at too rapid a rate or in a redundant fashion. Such behavior, upon uncovering, may be fixed by re-configuring or re-programming the client appropriately. (OPNET Corporation, Slides 46-59, 176-178 of “IT Guru QuickStart”, PowerPoint Presentation, 2004) Flow Analysis, Net Doctor and Discrete Event Simulation (DES) are IT Guru modules for all kinds of analysis and study of a constructed VNE. In other words, these modules assist with appropriately scrutinizing and playing with a virtual network. They are not tools for generating a topology and associated applications – rather they help in the further study of a given VNE. They are the analysis arms of IT Guru. IT Guru enables one to not only simulate a network but also to investigate such a simulation in depth. The preceding modules are each designed to probe different aspects of a VNE. The Flow Analysis module enables conducting studies on network traffic flows. In particular Opnet showcases report generation on IP flows and ATM flows in permanent network connection (PVC) scenarios. The module is capable of reporting on throughput, and routing algorithm and traffic flow behaviors. Connection failures are recognized and reported on. Flow Analysis would be 15 very useful in investigating what sort of impact changing network configuration may have on general traffic flow in a network. (OPNET Corporation, Slide 261 of “IT Guru QuickStart”, PowerPoint Presentation, 2004) The Net Doctor module can be used to check the configuration of various nodes in a network model. For instance suppose that a network’s routers are all supposed to behave a certain way. After one captures this network into a VNE (possibly via the VNE server) one can run Net Doctor to verify router configuration. If Net Doctor says that the VNE routers are not working as they ought to then that suggests that the real routers in the network are not behaving as they ought to. Net Doctor can find issues in routing, security, addressing and the like – one can program Net Doctor with how thin