EXERCISE 11.1 TROUBLESHOOTING A CONNECTIVITY ISSUEEXAMINE FIGURE 11.1....

5. unable to contact Computer B, then you have isolated the problem to 524ChApTEr 11: Network Troubleshooting Tools Computer B itself. Perhaps the network cable connecting Computer B to the network has gone bad, its network card has failed or needs a new driver installed or its IP configuration is incorrect.By approaching the problem systematically, you were able to trace the network connectivity from one end of the path (Computer A) to the other (Computer B). Testing at each step of the journey allowed you to isolate exactly where the problem was occurring.

Network discovery

Now, in a perfect world you’ll be administering a network that someone has already created detailed configuration diagrams for, so that you’ll know exactly what you’re working with when you need to troubleshoot a problem. In reality, though, we’re usually not that lucky, and network administrators often find themselves taking over networks that have little or no documen-tation in place, or documentation that hasn’t been kept up to date. Luckily, there are a number of tools that you can use to perform network discovery, which will help you to automatically generate documentation about the devices on your network and how they are configured. These network dis-covery tools will examine a single IP address or an entire subnet and gather as much information about the devices on that subnet as possible, including their IP addresses, Media Access Control (MAC) addresses, what type of operating system the device is running, and even what types of applications are installed on the device if it is a server or a workstation computer.There are a number of products available that will perform network dis-covery for you, though the majority of them are paid commercial software and

CoNFIGurING ANd IMplEMENTING

prioritizing Multiple Issues

to access any resources, and others are reporting

Sometimes, you’ll encounter a troubleshooting situ-

that their network access is only slightly slow, the

ation where you have several problems happening

all at once. In fact, this is not uncommon because

two problems may or may not be related. You should

troubleshoot the computers that are experiencing a

multiple problems will often be created by the same

total lack of network access first, because restoring

root cause. When multiple problems occur simulta-

neously, it’s important to focus on the problem that

network connectivity is more critical than removing

the occasional occurrence of lag on an otherwise

has the greatest impact on users. For example, if

some of your users are reporting a complete inability

working connection.

The OSI Model 525

FIGurE 11.2

SolarWinds IP Network Browser.

are not available as free downloads. One such product is Lan MapShot from Fluke Networks and another suite of tools is from SolarWinds that includes an IP Network Browser to perform automatic network discovery, as shown in Figure 11.2. If you are taking over a network that has poor or nonexistent net-work documentation in place, it’s strongly advisable to invest in one of these network discovery tools; the amount of time it will save you in troubleshoot-ing network connectivity issues will more than pay for the cost of the tool.

ThE oSI ModEl

As you have learned, the OSI model creates a framework that defines how networking protocols like TCP/IP communicate. Network packets are passed from the physical layer up to the application layer, with each layer adding its