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Subnetting and IPs IP addresses are an extremely important part of sending and receiving data across the Internet or across multiple networks. The IP address is the address assigned to each device and computer.

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Subnetting and IPs IP addresses are an extremely important part of sending and receiving data across the Internet or across multiple networks. The IP address is the address assigned to each device and computer. This public address is unique to that device and makes it possible to interact with and address that particular device. 32 bit IP addresses consist of two parts 1. the network ID identifies the network on which the host computer is found 2. the host ID specifies the specific device on the network IP's are displayed in Dotted Decimal Notation (DDN). This means that each group of 8 digits in a binary IP address (which is known as an octet) is separated by a decimal in its dotted decimal equivalent. IPv4 When IP was first created it was never envisioned that it would grow the way it did and so assigning a set number of digits for the network address and the rest of host addresses was perfectly reasonable for all networks. But soon, as IP grew in popularity, it was realised that many networks were being assigned too many hosts for their needs. This is how IP classes came about; they allow much more customisation in the number of hosts and networks available. There are five main classes: A, B and C being the most common and D and E being reserved for special purposes. Class A addresses are designed for the biggest networks. Only 8 bits at the start (and one of these is reserved to show that it's a class A address) ...read more.


This means that there is a much greater range of host device IPs instead of every network having 254, 65,000 or 16 million hosts. The problem with class allocation is that when a network needs move over the available host IDs, even if only by one device, a higher class is assigned. An example would be a Class C address which has 254 devices but wishes to add 10 more. This means a Class B address is required. This means that 65,000 host IPs are available but only 264 are being used. This means that well over 64,000 IP host addresses are being wasted! The second reason for subnetting is the large organisations that don't want to have all of their hosts on one physical network. With the use of broadcast addresses; it's possible to split the network down into much smaller physical networks with fewer hosts and still have the network work as a big network. Most of these networks are classed as supernets; which means they are subnetted outside of the usual classes- this is explained further in the next section. An excellent example of this is Google, and this is better explained in the example explained at the end of this document. For Google to have a single physical network would cause it to be slow and clumsy, instead Google relies on many servers scattered across the world. Google searches are sent to a broadcast address which is passed forward to the relevant addresses. ...read more.


Everything outside of the brackets is knocked down to the default 0 to find the network IP. When converted back to DDN we get This is Google's network address. To find out the host addresses, the same thing is done again except with the mask inverted. converted to binary is: 11011000.11101111.001(11001.01100011) The inverted mask is 13 bits: 00000000.00000000.000(11111.11111111) This leaves us: 00000000.00000000.000(11001.01100011) Translated back to DDN, this is: This is the number of hosts that Google has. So now it is possible to see that Google's server IP addresses start at and that this particular server has a (theoretical) host IP of This can be tested by adding and together, and sure enough this equals the original IP of The broadcast address for this subnet is This is the top of this range of addresses and is reserved for this purpose. To find the broadcast address of this network, we take the network IP we found earlier ( and apply the inverted subnet mask ( and carry out an XOR2 calculation. This is easily tested by carrying out a search for google.com online. The results are displayed below and show that the smallest possible address was the one first calculated and the biggest address is the broadcast address listed. 1 This is an and explanation, 2 XOR - compare two binary values. If just 1 of the values is 1 then the result is 1. If both are 1 or both are 0 then the result is 0. ?? ?? ?? ?? Page 1 ...read more.

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