Sams Teach Yourself TCP/IP in 24 Hours (4th Edition)

A protocol, as described in earlier hours, is a standard for communication. That standard is then implemented by a software vendor into a software module that performs the operations described in the standard. A human installs and configures the protocol software, either directly or by installing an operating system that supports the protocol software. As you might guess, once the software is up and running, the network still might not work. Sometimes certain services function and others do not. Other times, a computer can connect to one remote PC and not to another. Once in a while, a computer appears to have no network access at all, as if it weren't even connected.

Network dysfunction typically results from one of a handful of common problems. The TCP/IP community has developed a number of utilities for uncovering these problems and tracing a problem to its source. This hour discusses some of the common network problems and the tools you can use to solve them.

The top four network connectivity problems are typically some variation of the following:

• Protocol dysfunction or misconfiguration The protocol software doesn't work or (for whatever reason) isn't configured to operate properly on the network.

• Line problems A cable isn't plugged in or isn't working. A hub, router, or switch isn't working.

• Faulty name resolution DNS or NetBIOS names can't be resolved. Resources are accessible by IP address but not by hostname or DNS name (www.sun.com).

• Excessive traffic The network appears to be working, but it is working very slowly.

The following sections discuss tools and techniques for addressing these common connectivity problems.