Utilizing Diagnostic Tools

In the process of implementing and maintaining a network, there will be times when computers cannot communicate with one another and the problem must be isolated. There are a number of command-line tools that can be utilized to accomplish this. The purpose of these tools is to eliminate possibilities one by one until the smallest sets of possible causes exist, helping to determine and ultimately correct the problem.

Understanding the TCP/IP model can be a great aid when troubleshooting network problems. There are four possible layers where the problem can exist. As a review, the four layers and the types of problems that exist at those layers are as follows:

Application Layer Specific applications and services operate at this layer (DNS, SMTP, and so forth). If this layer functions, all other layers must be functioning, because this layer depends on all other layers for a connection. An example of a problem at this layer is the inability of computers to locate one another by name. This is a name resolution problem caused by the malfunction of DNS, an Application layer protocol.