IP Subnetting
Some folks consider this one of the most difficult hurdles to overcome in their IT learning process. Understanding the idea that one number has two parts that are arbitrarilly divided by yet another number is a strange concept, but one worth learning.
HOW TO:
How to subnet from Majorbacon: Subnetting.pdf
How to subnet one network in to many smaller subnets: 6 Steps to Easy Subnetting.htm
You-tube: Learn to subnet the easy way video: http://www.youtube.com/watch?v=C4n2Ofqr6QY&feature=related
Subnetting for new users from Cisco: http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a00800a67f5.shtml
Intro to subnetting from Microsoft: http://support.microsoft.com/kb/164015
Practice:
Practice questions: http://www.subnettingquestions.com/
Text based Subnetting Questions with answers from Majorbacon: SubnettingPracticeA.htm