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Ipv4 Final

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Ipv4 Final

1. 1. IP v4 Subnetting IPV4 IP Address Subnetting Made Easier “I HOPE” By Bill Donahue MS, CCNA, CCDA Solutions Design Engineer Version 1.0 1
2. 2. IP v4 Subnetting 1.0 Introduction IP v4 was developed in technical time a long time ago when it looked to have an unlimited supply of addresses available. With the ever increasing usage in IP addresses we have been waging a war ever since in order to preserve what little space is left. One of the techniques to optimize addresses is called subnetting. Network engineers must have a good understanding on how this is accomplished well beyond the use of a subnetting calculator. The goal of this whitepaper is to help simplify this using techniques I have learned from my years as both a Network Design Engineer and Faculty at ITT Tech. I will cover some of the basics that you should already have an understanding of and then review the technique that I have refined from my Cisco training and other classes on the subject. I will try to keep it on the lighter side so that you can easily read through. 2.0 Binary – Decimal or how do I count We as humans are used to counting by 10. Computers as computers are used to counting by 2. What engineers as the translators must be able to do is convert them back and forth with ease. No I am not going to spend any time explaining how the decimal system operates, if you do not understand this then STOP reading this paper now. Binary does require a little practice. Some of the basics definitions include: Bit – a single numerical value in binary either 1 or 0 Byte – Eight bits and a key value in the IP Addressing scheme that you must know In IP v4 Addressing understanding what the values are is key. In the Binary system just as in the decimal system the values increase from right to left with the Most Significant Bit being on the left. The difference is the Binary the powers increase by 2 not 10. Version 1.0 2
3. 3. IP v4 Subnetting So a byte with its eight bits would have the following values 27 26 25 24 23 22 21 20 What does this mean - each bit in the respective bit position starting from the right if it is a 1 will mean 2 raised to that power in that bit position and knowing the first 7 or being able to right them down like I have to do before any calculation is key. Here is a handy chart showing the decimal values of the above numbers 27 = 128 26 = 64 25 = 32 24 = 16 23 = 8 22 = 4 21 = 2 20 = 1 When doing any conversions of a byte value I would recommend writing these numbers across the top of a piece of paper and then filling in the respective decimal value for each “1” in the byte for the bit position. Add them all up and you have your decimal equivalent to the Binary value. Reversing our trend here and going from decimal to binary is just as easy except we use subtraction and start on the left or with the most significant bit and keep subtracting the decimal value and reducing our number until we reach zero. Seeing is believing so let’s go over some examples of this so that you understand this very important IP addressing step. 2.1 Binary to Decimal DO NOT TRY TO DO THIS IN YOUR HEAD MISTAKES WILL HAPPEN Let’s try this byte value 10101010 and convert it to decimal Remember the first part of this is to put the eight bit place values down on the top of the paper like this: 128 64 32 16 8 4 2 1 You can then insert the binary number below and in each bit position that is a 1 we add the decimal value up to come up with a total lets see what happens on the next page. Version 1.0 3
4. 4. IP v4 Subnetting Remember our byte value is 10101010 so 128 64 32 16 8 4 2 1 1 0 1 0 1 0 1 0 Gives us - 128 + 32 + 8 + 2 = 170 in decimal A couple more examples 10110111 in binary 128 64 32 16 8 4 2 1 1 0 1 1 0 1 1 1 128 + 32 + 16 + 4 + 2 + 1 = 183 11111111 in binary 128 64 32 16 8 4 2 1 1 1 1 1 1 1 1 1 128 + 64 + 32 + 16 + 8 + 4 + 2 + 1 = 255. ****** This is actually an extremely important value to know – IF ALL BITS are 1 then the value is 255, you will see later why this is an important value to memorize. Version 1.0 4
5. 5. IP v4 Subnetting 2.2 Decimal to Binary Now let’s reverse direction and go from decimal to binary values again we want to have our scale across the paper and let’s start with 188 as a decimal value that we want to convert to binary. We start by subtracting the highest value and repeating until we are at 0. 128 64 32 16 8 4 2 1 Starting with 188 we subtract 128 leaving 60 then we subtract 32 because 64 does not fit and we repeat all the way to zero – here it is using basic arithmetic 188 – 128 = 60 60 – 32 = 28 28 – 16 = 12 12 – 8 = 4 4–4=0 Now putting in our “1” values we get 128 64 32 16 8 4 2 1 1 0 1 1 1 1 0 0 Another example lets try 207 207 – 128 = 79 79 – 64 = 15 15 – 8 = 7 7–4=3 3–2=1 1 -1 = 1 Gives us 11001111 as seen below 128 64 32 16 8 4 2 1 1 1 0 0 1 1 1 1 Version 1.0 5
6. 6. IP v4 Subnetting 3.0 IP v4 Basics IP version 4 consists of 32 bits broken down into four groups of 8 bits (byte) separated by a period. These bits are then written down as a decimal equivalent number so that humans can read. Hence the reason why we as engineers must be able to convert back and forth. Try reading the following same value and figure which is easier to understand 10100011.11111111.00000001.11001100 in binary or 163.255.1.204 in decimal As you can see the second value is much easier to understand. Now what does this number mean not much unless you understand a key point. That is, some of this number represents a network address and some of this number represents a host address. Where this separation takes place is of critical importance and can change via subnetting so lets work through the steps to get there. 3.1 Basic IP Address Classes In the world of IPV4 there are 4 classes of IP addresses that network people need to be concerned with (in reality there are 5 classes). For simplicity they are Class A-D and experimental 5th class (Class E). These are referred to as the Classful boundary and separate the network portion and host portions of the network. It is this boundary that we are manipulating with subnetting to adjust our line of demarcation to allocate more or less hosts. These classes are broken down based on address numbering in the first byte as follows Decimal Range Binary Value Host Bits Class A – 0 – 126 0xxxxxxx 24 Class B – 128-191 10xxxxxx 16 Class C – 192-223 110xxxxx 8 Class D - 224-240 1110xxxx (Multicasting) Note: you may notice that there is no 127 value listed between the Class A and B addresses. That is because the value is reserved for Loopback purposes and cannot be used for general network addressing. Version 1.0 6