The Penguin's Practical Network Troubleshooting Guide
Start with Cable Testing
Linux has everything you need to do any kind of networking, plus it has eleventy-eight hundred different software utilities for network monitoring and troubleshooting. Today we'll learn how to pinpoint connectivity problems and how to map your network and all running services. This is handy not only for keeping tabs on everyday activities, but also to catch users running illicit hosts and services.
There are so many different software utilities it's easy to get lost and not know what to use, and there is a lot of overlap in functionality. So we're going to focus on
nmap. Doubtless someone will tell you their own favorite way of doing things that is different from yours, and it is always good to know these things, but it doesn't mean they are superior. Just different.
Warning: Take care to not be abusive with network testing software. Use
tcptraceroutejudiciously, and be very careful with
nmap, because most admins consider
nmapscans to be hostile acts. Unless you have a good reason and permission, never run
nmapon any network but your own.
Way back in olden times, Enterprise Networking Planet (like LinuxPlanet, a JupiterWeb site) ran an article on testing Ethernet cabling. Nothing has changed in the cable-testing world, so this article is still useful. Consider today's offering a somewhat belated followup.