Part 2

As mentioned prior to this, one of the key elements to subnetting is Binary, Octal, Decimal, and Hexadecimal conversion.  While I do like the Sybex Study Guide for CCNA by Todd Lammle, I do believe with respect to the subnetting aspect there are other better resources.  For example the Bryant Advantage system, the ICND 1 & 2 Study Guides for CCENT & CCNA by Wendell Odom (especially the Appendicies), and Test King (  I am certain that there are others, but I have come to an appreciation and an understanding after these; of course, the CCNA Bootcamp was an extreme help as well!

One trick that has stuck with me is this:  Key on the first several digits to the first segment of the IP Address (i.e.,,,,, &

10   = 00001010 = A first four digits 0000-0111

172 = 10101100 = B first two digits 1000-1011

192 = 11000000 = C first two digits 1100-1101

224 = 11100000 = D first four digits 1110

240 = 11110000 = E first four digits 1111


This is a quick assessment trick which can cut off some time while determining to what subnet class the address is a part of.  Of course, it is just as easy to memorize the entire spectrum.

Here are some IPv4 Subnet Cheat Sheets that you may find helpful:,,,,,;_ylu=X3oDMTE1ZWJyN2IxBHNlYwNzcgRwb3MDMTcEY29sbwNzazEEdnRpZANRSTAyNl8xMzQ-/SIG=143bk83dn/EXP=1361929573/**https%3a//,

Look through some of these cheat sheets, you may pick something up from them; on the other hand, you may already know it – to which I say GREAT!


Some questions you need for determining subnets, hosts, etc.:

  1. How many subnets?  2= number of subnets (x is the subnetted masked bits or 1’s; 11000000 2 ones = 22 = 4 subnets)
  2. How many hosts per subnet?  2y-2 where y is the number of unmasked bits or 0’s; 11000000 = 26-2 = 64-2 = 62 hosts.
  3. What are the valid subnets?  256 – subnet mask = block size or increment; 256 – 192 = block size of 64.
  4. What is the broadcast address for each subnet?  Our broadcast address is the last address prior to the next subnet; i.e., our block size is 64 then our starting addresses are 0, 64, 128, 192…therefore, the broadcast address would be the on prior to the last which is 63, 127, 191, & 255.
  5. What are the valid hosts? The valid hosts are all of the addresses in between the subnet and the broadcast addresses; i.e., with the block size of 64 then our valid hosts are: 1-62, 65-126, 129-190, & 193-254.

See also:  Part 1, Part 2, Part 3, Part 4

Works Cited

Lammle, T. (2007). CCNA Cisco Certified Network Associate Study Guide. Indianapolis: Wiley Publishing, Inc.

Odom, W. (2012). Official Cert Guide ICND1 640-822. Indianapolis, IN: Cisco Press.

Odom, W. (2011). Official Cert Guide ICND2 640-816. Indianapolis, IN: Cisco Press.



Part 1

I have been debating how to approach this subject of Subnetting, there is not much to say other than it really sucks to learn.  But once you learn it, it just gets easier and more understandable.  Unfortunately, every new subject you learn, with which you have no familiarity with is going to be absolute hell unless you can pick it up quickly.  When I started learning subnetting and then relearned and re-familiarized myself, I have to admit it was tough and I just was not getting it.  But the information super highway, Youtube, and many other tid-bits of information out there in the world can make all the difference in the world.  You might not understand what one method teaches there is always another method that may take hold in your brain.  So, take heart…it may be a roller coaster, but it is our roller coaster.  Just keep looking for the method that makes sense to you, it is out there.  Below are some references, which are not all inclusive as there are a multitude more references for your viewing pleasure.

Youtube, as you probably already know, is an underutilized resource and valuablesubnet-study tool in your arsenal of learning.

Look through these references, videos (you won’t need to view all, just until you are comfortable), and the other web-sites.  To really prepare yourself for the test (CCENT or CCNA) use the IPv4 subnetting – random question generator v1.6  as it will generate random IPv4 subnetting questions for you to practice on (makes it easy for you!)

headerfistAlso, keep in mind that you will be tested on IPv4 for subnetting, so that is what we will be using.  IPv6 is being deployed and you may see it on the test for CCNA, but more likely than not you will not receive test questions on the subnetting of IPv6.

Until we meet again in Part 2…

See also:  Part 1, Part 2, Part 3, Part 4



Other Web-Sites:

IPv4 subnetting – random question generator v1.6