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The tone generator sends a signal across one pair of wires in a UTP cable…

Never hook a tone generator to a cable that is hooked up to either a NIC or a hub! Because the tone generator sends electrical signals down the wire, it can blow a NIC or a hub. That is why tone generators are not usually used on networks. Cable testers are used more often. We’ll discuss cable testers later in this chapter.

Software Troubleshooting Tools

In addition to these hardware troubleshooting tools, you can use software programs to gain information about the current health and state of the network. These tools fall into two main categories:

■    Protocol analyzers

■    Performance-monitoring tools

We use the term network software diagnostics to refer to these tools.

Protocol Analyzer

Any software that can analyze and display the packets it receives can be considered a protocol analyzer. Protocol analyzers examine packets from protocols that operate at the lower four layers of the OSI model (including Transport, Network, Data Link, and Physical) and can display any errors they detect. Additionally, most protocol analyzers can capture packets and decode their contents. Capturing packets involves copying a series of packets from the network into memory and holding the copy so that it can be analyzed.

You could, for example, capture a series of packets and decode their contents to figure out where each packet came from, where it was going, which protocol sent it, which protocol should receive it, and so on. For example, you can find out:

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