![]() As the guy got more successful he had to figure out a way of putting the bricks in piles so it would be quick and easy to give them the number of bricks they wanted. He had a lot with a lot of bricks and people would come and buy bricks. I had a teacher (Jeremy Cioara – he has written several Cisco books) and he gave the story of a guy that owned a brick company. Look to the subnet mask column and you see that it is. Counting to 27 would get you to the third most significant bit (32). You know that the sum of the first three octets is 24 so you start counting 25 with the first bit (128). Where the chart comes in handy is if you are being asked what the subnet mask would be for /27. To arrive at the subnet mask we can do one of two things, add the positive bits together or take the least significant positive bit and subtract it from 256. If you are looking at a network you can have a network address of 192.168.17.0. If you are wondering how we get 256 in one octet, there is an implied zero at the end. If you add up all of the bits it comes to What the chart represents are the eight bit values of one octet of an IPv4 IP Address. When you are going to take a Cisco exam, before the exam starts write the following information down (public and private class address ranges and then the chart) as it will save you a lot of time and headaches.Ĭlass A: 1 – 126 (127 reserved for loop-back and diagnostic tests) Class B: 128 – 191 Class C: 192 – 223 Class D: 224 – 239 (reserved, used primarily for IP multicasting) Class E: 240 – 254 (reserved, experimental) Private addresses – Class A: 10.0.0.0 through 10.255.255.255 Class B: 172.16.0.0 through 172.31.255.255 Class C: 192.168.0.0 through 192.168.255.255 128 Special Thanks to Mimi Shaw for contributing these shortcuts! ![]() Need some help with Subnetting? Preparing for your CCNA Exam? In this multi-page list of Subnetting Shortcuts, you will find tricks, tips, and test preparation know-how when it comes to IP Subnetting, Check it out! ![]()
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