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Troubleshooting a network

A paralyzed network can cost an organization oodles of time and money. Here are some handy tips to help you trace and rectify any network-related problems By Mahesh Rathod

One of the most important
precautions to minimize network collapse is to insist on reliable network designs based on the official configuration guidelines. However, since a network is a conglomeration of numerous components and devices, something is bound to go wrong somewhere, somehow even in the best of networks.

There are numerous reasons why your network can go down, but there are a few basic approaches to troubleshooting that can help you locate the problem faster.

One of the best ways to avoid unnecessary network downtime and improve reliability is to make sure that your network cabling and signaling system reach the predetermined standards and are built accurately using quality components. A number of surveys have revealed that about 80 percent of network failures are related to the network medium: the cables, connectors, and hardware components that make up the signal-carrying portion of a network. Many problems with media systems are due to improperly installed hardware, the use of incorrect components, network designs that violate official guidelines, or a combination of all three.

Following a Troubleshooting Model
Troubleshooting a network problem is a combination of the scientific method and the technique of 'divide and conquer'. The scientific method is where you formulate a hypothesis and then test it. Using your knowledge of the symptoms and your knowledge of how networks operate, you form one or more hypotheses to explain the behavior of the network, and then you perform tests to see if those hypotheses hold up.

The following steps will guide you in troubleshooting your network.

Discover the problem. This is the fault detection stage, in which you are notified of a problem. Notification may be done by automatic fault detection software, or users may call you with a problem report.

Gather facts. This is a process of acquiring information about the problem. This is rather like the game of "Twenty Questions" in which you ask leading questions to try and discover information.

Create Hypotheses. Based on the facts you have gathered and your knowledge of how networks function, you should be able to create one or more hypotheses about the source of the problem. While doing so make sure you do not overlook the obvious. Test the obvious hypothesis first, before spending time on more complex theories. Try to avoid jumping to conclusions, and do not make unnecessary assumptions about the cause of the problem. Make sure that the hypothesis you create can adequately account for the symptoms and other information you have collected.

Develop an action plan. At this stage you may have enough information to begin tests of a given device on the network. A test might be as simple as replacing the device with a spare, and then checking to see if the problem was resolved. Or, at this stage you may need to further isolate the problem, in which case your action plan may include some variety of 'divide and conquer', or binary search, which is described later.

Implement your action plan. When troubleshooting a problem, try to make only one change at a time. The goal is to eliminate suspected problems one at a time, to limit the number of things you are trying to test and evaluate at any given moment. This way, you can avoid losing track of the problem by trying to evaluate too many things at once.

Test and observe results. After making a change in the system, you need to test and observe the results, to make sure that you have resolved the problem. If your action plan was based on a binary search, then the test should show you whether the problem is still active, or whether it is now located in the portion of the network that you have isolated as part of the binary search.

Repeat the troubleshooting process. If the symptoms still persist, you need to repeat the process until you have resolved the problem.

These tips will help you troubleshoot your network the next time it gives a problem. Check this column for more interesting topics in the coming issues.

Troubleshooting a network using Qcheck
Qcheck is a free utility that provides network performance measurements and helps in troubleshooting. It can be downloaded at www.qcheck.net and consists of two software components: a console with a graphical user interface, and distributed software agents called Performance Endpoints (or simply, "endpoints").

The Qcheck console is where you configure and run tests and then view test results. You can select among several kinds of tests, together with the addresses of the endpoints and the protocol to use between them (TCP, UDP, SPX, or IPX). The test results are summarized in a window, while a more detailed report of test results can be viewed in a Web browser.

What performance indicators does Qcheck measure?
Qcheck gives a quick check of the response time, throughput, streaming capability, and routes between a pair of computers in a network. Depending on the application and user, different measurements reveal a lot about overall network performance.

Key measurements for most business and Web transactions are response time and throughput. When an answer or reply is needed quickly or frequently, users worry about response time. When large files must be transferred quickly, throughput is the primary concern. Users of streaming applications need to know that a network can support a fixed level of throughput. They also have an additional concern: how many data packets are lost as the data is sent from the sender to the receiver. The lost data information Qcheck provides can help determine a network's readiness for streaming multimedia traffic.

Finally, traceroute information can show performance bottlenecks and slowdowns at intermediate nodes. When latency is important, either as a component of response time or for real-time streaming applications such as VoIP, traceroute can show the paths in each direction and the round-trip time to each hop on the paths.

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