ACHAPTER 11NETWORK TROUBLESHOOTING TOOLSEXAM OBJECTIVES IN THIS CHAPTERA TROUBLESHOOTING METHODOLOGY 520THE OSI MODEL 525WINDOWS TOOLS 529LINUX TOOLS 553NETWARE TOOLS 557OTHER NETWORK TROUBLESHOOTING TOOLS 558IMPORTANCE OF NETWORK DOCUMENTATION 56...

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ChApTEr 11

Network Troubleshooting Tools

ExAM oBJECTIvES IN ThIS ChApTEr

A TrouBlEShooTING METhodoloGy 520ThE oSI ModEl 525wINdowS ToolS 529lINux ToolS 553NETwArE ToolS 557oThEr NETworK TrouBlEShooTING ToolS 558IMporTANCE oF NETworK doCuMENTATIoN 561

INTroduCTIoN

Throughout this exam guide, we’ve talked about the fundamentals of network protocols and network operating systems. In this chapter, we’ll bring together that knowledge to help you in troubleshooting any errors or problems that occur on your network. We’ll begin by talking about the overall methodology that you’ll use to troubleshoot a network. This begins with gathering infor-mation about a problem to try to determine its cause. You’ll then use your understanding of networking concepts as well as your knowledge of how your particular network is configured, to isolate the point where the problem is occurring. By eliminating points of failure in a systematic fashion, you can eliminate trouble spots one by one, until you’ve located the cause of the problem. Maintaining accurate documentation of the physical layout of your network is essential for this process, as is having a firm grasp of the layers of the Open Systems Interconnect (OSI) model and the devices that operate at the various layers.To help you in troubleshooting your network, there are many software utilities for both the Windows and Linux operating systems that will assist you in pinpointing the exact nature of a failure. You’ll start with tools that will test basic network connectivity to determine if two computers can 519communicate with each other in any way. You can then move onto more 520ChApTEr 11: Network Troubleshooting Tools detailed tools that will show you every aspect about the path that a network packet takes to travel from one computer to another, or to gather detailed information about name resolution issues. You also have access to a wide range of testers for physical network components such as network cables and wall jacks. By combining a broad understanding of networking concepts with specific knowledge of the different troubleshooting tools available to you, you will be able to effectively troubleshoot any issues you might face when administering a network.

A TrouBlEShooTING METhodoloGy

Before we talk about specific tools and utilities that you can use to trouble-shoot your network, it’s important that you have an overall structure in place that will help you perform that troubleshooting. Unfortunately, networking technologies haven’t advanced to the point that a router will flash up an error message like, “My default gateway is misconfigured, please correct this.” Instead, it is up to you to determine what a problem is before you’ll be able to go about fixing it. When you’re troubleshooting a problem relating to network connectivity, you need to have an understanding of your network as a whole so that you can determine where the trouble is occurring. One of the key factors in network troubleshooting is isolating the issue to figure out whether it’s being caused by a single workstation or cable, or if it’s a larger issue affecting numerous users on your network.You can break down the troubleshooting process into two major steps:Gathering information

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Analyzing the information you’ve gathered

Gathering Information About a problem

To troubleshoot a problem, you first need to identify the problem. This can be a challenge when you’re trying to gather information from different users on your network, especially if you’re dealing with a situation where you’re receiving reports of multiple problems at the same time. You need to determine which component of your network is causing the issue; this can be a physical component like a network cable, or a logical component like the Internet Protocol (IP) configuration for a particular network interface card (NIC). You’ll use the information you gather to determine which component of your network has failed or is misconfigured.A Troubleshooting Methodology 521Your first step should be to gather information from your users about the nature of the problem. Some questions you’ll probably want to ask include the following: