1 Internet Protocol V4 Addressing & Subnetting Written by Bill Reed 22/02/04
2 We will Look at the structure of an IP V4 address. Examine the Binary principles behind an IP V4 address.Identify the historic classes of IP V4 addresses.Divide an IP V4 address into subnets.
3 IP V4 Address Structure Notation IP V4 Addresses are represented in a way known as DOTTED DECIMAL NOTATIONAn example of this could beEach Decimal number represents a BINARY BYTE and therefore is limited to a value between 0 and 255
4 IP V4 Address Structure Hierarchical IP V4 Addresses are hierarchical in natureThink of a postal address.The first Decimal number could represent a country.The second Decimal number could represent county.The third Decimal number could represent a post code denoting a town, an area of that town and a street.The fourth Decimal number could represent a house number on that street.An advantage of hierarchical addressing is that additions can easily be made, for instance we could build another few houses in our street and give them numbers without effecting upper layers of our addressing structure. We call this scalability.
5 BINARY PRINCIPLES How Binary values work BINARY BIT VALUESEight BITS = 1 BYTE or OCTETIf all eight values in a BYTE are added together they come to a value of 255
8 How Binary values workBINARY BIT VALUES128192224
9 How Binary values workBINARY BIT VALUES128192224240
10 How Binary values workBINARY BIT VALUES128192224240248
11 How Binary values workBINARY BIT VALUES128192224240248252
12 How Binary values workBINARY BIT VALUES128192224240248252254
13 How Binary values workBINARY BIT VALUES128192224240248252254255
14 DOTTED DECIMAL NOTATION RECAPIP V4 addressing is represented usingDOTTED DECIMAL NOTATIONEach DECIMAL number represents a BINARY BYTEA BINARY BYTE can represent a value between 0 and 255IP V4 addressing is hierarchical and therefore scalable
15 The Historical IP V4 Address Classes Class A range = – BIN 0???????0 = = (16,777,214 available addresses)Class B range = – BIN 10??????128 = = (65,534 available addresses)Class C range = – BIN 110?????192 = = (254 available addresses)
16 Dividing an IP V4 address Subnetting IP V4 addresses have things called default subnet masksSubnet masks tell some networking deviceshow we want to divide our address spaceA class A default subnet mask looks likeA class B default subnet mask looks likeA class C default subnet mask looks likeWe subnet to gain additional discrete network addresses from a single address space.Discrete network addresses are advantageous for security and organisational reasons.
17 Dividing an IP V4 address Subnetting CASE STUDYDividing an IP V4 address Subnetting= ONE NETWORK with 254 available addressesOur client has bought this class C address space from her ISP.Our client has a building with 5 floors.Our client needs a different network address space on each floor.HOW DO WE ACHIEVE THIS AND SATISFY OUR CLIENT?
18 Dividing an IP V4 address Subnetting CASE STUDYDividing an IP V4 address SubnettingFirstly we identify the address class.Next we identify the default subnet mask.Then we get out our DIY subnet calculator.
19 CASE STUDYDIY subnet calculatorWe inform the network devices that we want to divide upOur address space by specifying a subnet mask that borrows BITS from the host portion of the address space.128192224240248252254255BINARY valuesAccumulated BIT values
20 CASE STUDYDIY subnet calculatorRememberWe need5 subnetsIP V4 addressSubnet mask128192224240248252254255When we subnet using the no math methodwe start from the right hand side.We move left along the numbers until weSee a number larger than the amountof subnets that we need (8), this will be the numberOf subnets that we create.Next we count how many BITS are to the rightOf this number (in this case there are 3 BITS)This is the number of BITS we must borrow.
21 CASE STUDYDIY subnet calculatorIP V4 addressSubnet mask128192224240248252254255So far we have established that we need toBorrow 3 BITS from the host portion of theAddress.Now we need to specify a subnet mask that tells the network devices of our intentions.We achieve this by changing the DECIMAL value in the host portion of our subnet mask to a value that represents 3 BINARY BITS added together.
22 CASE STUDYDIY subnet calculatorIP V4 addressSubnet maskNew subnet mask128192224240248252254255So far we have specified a subnet mask to create 8 subnetsWe borrowed 3 BITS from the RHS to achieve thisNow we must find out how many addresses are available inside each of those subnets.We do this by counting from the LHS the number of BITS borrowed (3) and taking 2 away from this number.32 – 2 = 30
23 DIY subnet calculator That’s it we are done! CASE STUDYDIY subnet calculatorRemember 32 was our spacing for the subnetsOur eight subnet addresses are:That’s it we are done!Now you know how to subnet!An interesting aside is that the last octet of the last subnet address, matches the last octet of the subnet mask. (this will always be the case no matter what the subnet mask)