8.2. Host-Monitoring Tools

We have already discussed host-monitoring tools in several different parts of this book, particularly Chapter 2, "Host Configurations" and Chapter 4, "Path Characteristics". An obvious example of a host-monitoring tool is netstat. You will recall that the -i option will give a cumulative picture of the traffic into and out of a computer.

Although easy to overlook, any tool that logs traffic is a host-monitoring tool of sorts. These are generally not too useful after the fact, but you may be able to piece together some information from them. A better approach is to configure the software to collect what you need. Don't forget applications, like web servers, that collect data. Accounting tools and security tools provide other possibilities. Tools like ipfw, ipchains, and tcpwrappers all support logging. (Log files are discussed in greater detail in Chapter 11, "Miscellaneous Tools".)

Host-monitoring tools can be essential in diagnosing problems related to host performance, but they give very little information about the performance of the network as a whole. Of course, if you have this information for every host, you'll have the data you need to construct a complete picture. Constructing that picture is another story.

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