Hi! Great info here, but i'd like to add a note of caution to two things:
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Routers and Cable Modems
Turn off your devices and wait one minute. If you have both a modem and a router, turn the cable modem on and wait until all the lights stabilize. Turn the router on after about two minutes.
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Sadly, this can be dead wrong. Frex, if you're a home machine with a dynamic IP on your router, chances are high that the modem is assigning an IP via DHCP to whatever MAC it sees when it powers up.
English? If the network connection is being annoying, then all your stuff should be on FIRST. Power everything down; power up your router and your computer; after that's done, power up the cablemodem. The modem will see your router and say "oh hi, i remember you, here's your IP." If you're lucky enough to have missed a lease renewal or suchlike, and the modem powers up first seeing nothing, your router's IP will be nothing. Bleah.
Secondly, NMAP and similar:
Do not go blasting around your network with NMAP haphazardly, or at least without warning someone... ESPECIALLY if you're on some kind of academic network! Before you scoff, please allow me to introduce you to a long list of students who got access revoked or outright expelled for being "hackers," due to the idiocy of ignorant administrators. If you Nessus or NMAP your way around your campus, especially not knowing how easy it is to turn on "Full Frontal Assault" mode, you may trip some alarms and/or scare some people. Be careful.