22 February 2014
Ken Long - klong13@cnm.edu or kenglong@gmail.com

Subnetting as Taught at Central New Mexico Community College

One of the most important skills one needs to learn to become a Network Administrator is subnetting. These pages show what I've learned at CNM on this subject. In all of my classes so far, I've been taught the bare-bones way to subnet. That means using binary math, bit-wise ANDing, and conversion between binary and decimal. While this may appear extremely complicated to some people, learning to do it this way illustrates the "why" of the process in ways that those shortcuts and tricks can never do. If you learn how it works you'll be way ahead of the game.

Here are some pages that I threw together during the Spring 2013 semester while taking Cisco 1:

The step-by-step procedure I learned.

A practical subnetting problem.

A challenging subnetting problem from the book.

Fast forward to August 2013 and I find myself reviewing subnetting for the Cisco 2 and Cisco 3 courses I'll be taking this fall. While doing some practice problems, I found I had forgotten a few things. Here are some pages that show my mistakes and explains how I should have done it.

Mistake #1 from David Clauss' IP Subnet Problem Generator

Mistake #2 from David Clauss' IP Subnet Problem Generator

I now find myself in Spring 2014, my last semester, and I need to review some new subnetting subjects I learned last fall and some new subjects.

Subnetting Charts

Route Summarization

Route Summarization in Reverse

ACL Wildcard Masking

Lastly, here are links to other subnetting sites:

IP Subnet Problem Generator (David Clauss)   

Note: Can hit “repeat” on the subnet problem generator page to get a new ip address. You can enter a specific IP address and get a problem on that one. Like this: http://david.clauss.us/Subneting/index.php?A=16&B=244&C=61&D=173&S=12

Multi-mask Subnet Problems (David Clauss)

A basic GNU Subnet Calculator (this one does wildcard masks!)

A more full-featured Subnet Calculator

Subnetting Practice and Game

Subnetting Tutorial

Old CNMNorth

New CNM North (as of April 2014)


Thanks to David Clauss, James Hart, David Beach, Steve Perry, and Bob Hennigan at Central New Mexico Community College for taking me this far. I'm sure I'll refine this as more of the steps become second nature and I more fully understand the underlying mechanics of it all.