IP Subnetting - Cheatsheet

welcome to teaching IP subnetting this presentation is derived from the book IP subnetting made easy by john kowalski which is available amazon.com while this presentation is derived from copy written material free distribution is encouraged the purpose of this video is to aid IT instructors in the teaching of the cheatsheet method found in IP subnetting made easy this presentation details only the most critical part of the book not the entire book before revealing the cheat sheet method you must teach your students what is commonly called the bit method of subnetting this ensures that they know the basics of how network devices manipulate their network addresses as we can see here the cheat sheet consists of two main columns of information the first column lists the subnet bits used either for network or for hosts the second column lists the powers of two the subnet bits portion can be recreated simply by numbering 1 through 8 on a piece of paper these represent the bits used in a subnet mask for the network the center row depicts the possible masks if a student knows binary this is Elementary in the case of the first line 128 is a product of one network bit followed by seven zeros line two is simply two network bits and six zeros line three consists of three Network bits and five zeros and so on the third column represents the host bits as these are merely the bits of a given octet that are left over from the network portion the formula is simply 8 - the first column finally the last column is simply the powers of 2 2 to the power 0 through 2 to the power of 10 is shown and it's usually all that is needed for most subnetting problems remember before presenting this method you should have already taught your students the concepts of binary variable length subnet masks and other subnetting foundation topics via either IP sub then he made easy or via your own method let's begin with a practical example given a Class C address what is the subnet mask needed to provide at least 12 hosts per subnet let's recreate the cheat sheet first off we look at the powers of 2 side and see that 16 will yield at least 12 hosts per subnet 16 is a product of 2 to the fourth power since we ask for hosts we will look over to the subnet bits portion on the host side and find the corresponding 4 as in 2 to the 4th power now we know from the question that it's a Class C address so that the mask is going to be 255 dot 255 dot 255 dot something by using the cheat sheet we find that that something is 240 therefore the answer is 255 dot 255 dot 255 dot 2 40 let's try another example given a Class C address what is the subnet mask needed to provide at least 50 hosts per subnet looking at the powers of two on the cheat sheet we see that two to the sixth will yield 64 hosts since we ask for hosts we will turn again to the host side and look down the column for the number six as in two to the sixth we know that a Class C address once again is 255 255 dot 255 dot something the cheat sheet tells us that 192 is again that's something therefore the answer will be 255 dot 255 dot 255 dot 192 let's try a little different question this time given a Class C address what is the subnet mask needed to provide at least 20 subnets again we follow the cheat sheet look at the powers of two and see that 2 to the 5th will yield 32 this time however we will look at the network side of the cheat sheet since we asked for subnets we find a corresponding number 5 as in 2 to the 5th and see that a 248 mask is required therefore the answer is 255 dot 255 dot 255 dot 2 48 here's another Network question but with a Class B address given a Class B address what is the subnet mask needed to provide at least 100 networks the power is a two table tells us that two to the seventh will fit our needs if we look on the network side and go down to number seven we see that a 254 mask is required since we know that a Class B address begins with 255 dot 255 the answer is 255 dot 255 dot 255 dot 0 let's use the cheat sheet to try to solve a two-part question the question is will a Class C address with a 27 bit mask provide at least 6 subnets with a minimum of 20 hosts per subnet let's look up the subnets first 2 to the 3rd will yield 8 and the corresponding 3-wheeled a to 24 mask this is a 27 bit mask how do we know this a Class C address is a 24 bit mask adding 1 to 3 to that equals 27 we see that we have five bits left over for the host on the powers of two side 2 to the 5th equals 32 is 2 to the 3rd greater than or equal to 6 and is 2 to the 5th greater than or equal to 20 the answer in this case is yes here's a similar question will a Class C address with a 26 bit mask provide at least three subnets with a minimum of 70 hosts per subnet we'll begin by looking up the subnets to to the second will yield four on the network side of the cheat sheet we see that two yields a 192 mask leaving six bits per host two to the six equals 64 is 2 to the second greater than or equal to 3 and is two to the sixth the greater than or equal to 70 the answer in this case is no let's try one more two-part question given a Class B address what mask is needed to yield 50 networks how many hosts per subnet will this mask yield two to the six will give us 64 if we look on the network side we see that 6 corresponds to 252 so the answer to the first question is 255 dot 255 dot 255 10 bits left over that is 8 from the fourth octet and 2 from the third octet 8 plus 2 being 10 2 to the 10th equals 1024 as we have seen the cheat sheet is the heart and soul of IP subnetting made easy why not teach it first there are many underlying concepts that are needed to fully understand subnetting these are covered completely in the book this presentation only covers a cheat sheet method IP subnetting made easy was designed by an IT instructor specifically for IT students it is inexpensive comes in a convenient format and it's very easy to read and understand for bulk orders for your class contact the author @j KO w al s ki at SC 42 you individual copies are available via hard copy or via kindle at amazon.com thank you for considering using IP subnetting made easy as an add-on book to your curriculum I will leave you with some you reader comments you

Channel: Networking 101

Views: 103,387

Rating: 4.9348078 out of 5

Keywords: IP Address (Protocol), Information Technology (Industry), IP subnetting

Id: Am-O4rZCb8I

Length: 11min 37sec (697 seconds)

Published: Sat Oct 19 2013