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As mentioned under Understanding IPv4 Addressing System, human prefer to deal with Decimal over Binary System. Understanding Class A Network IP Addresses explains why the previous article suggested to use 256 decimal to represent the Binary Network 0.0.0.0 (The ONE Big Pie) as base to divide, therefore, decimal 256 can be divided as needed. Let’s start the fun of reverse engineering to show you how decimal 256 was divided to form the Classful A Networks.
Table of Contents
Creating Class A Networks
As mentioned in my previous article, First byte of Network 0.0.0.0 equal to 8bits of zeros, therefore, 28 = 256. Now, 256 can be used as the Original Network for the Engineers to divide into smaller networks using decimal number.
Since Binary Base 2 System must be used, then dividing 256 by 2 will divide the Original Network 0.0.0.0 into 128 Networks, which means half of the IP Space has been distributed among the 128 networks.
As a result of this division, Class A Networks are formed starting by Network 0.0.0.0 up to 127.0.0.0, that is 128 Networks, however, Network 0.0.0.0 and 127.0.0.0 can’t be used.
256 / 2 = 128 as Remainder, and since computers count from 0, then the last number is 127, and 128 would belong to the next Class – B Networks.
Note: Network 0.0.0.0 can’t be used as well since it’s Zeros. Besides, Network 127.0.0.1 was reserved for loop back address, so we left with 126 Classful A Networks, which start from 1.0.0.0 up to 126.0.0.0 Network.
Presenting Class A Networks
1.0.0.0 up to 126.0.0.0 Network can be used. Class A known by ruling the first byte, the last 3 bytes dedicated for IP Addresses.
Public Range
Example of Class A Public IP Address Range
1.0.0.1 up to 1.255.255.254
Another IP Address Range from the last Class A Network
126.0.0.1 up to 126.255.255.254
Private Range
Class A Private Network dedicated for internal usage.
10.0.0.0 with broadcast 10.255.255.255
Example of Class A Private Usable IP Address Range
10.0.0.1 Up to last IP Address 10.255.255.254
Calculate Usable IP Addresses
Since Class A rules the first byte, we left with 3 bytes for the Hosts.
Hosts = 224 = 16,777,216 – 2 = 16,777,214 Hosts or Usable IP address Per Network!
126 Networks x 16,777,214 = 2,113,928,964 (2 Billion something Usable IP addresses)
Based on 128 / 256 =.50, Class A IP addresses represent almost 50% of the Original IP Space Total.
IP Address Experiment 3 Layout
This Experiment will use 1.0.0.0 as Network Address, and 1.255.255.255 as Broadcast Address.
Sam’s IP address:
IP Address: 1.0.0.1 00000001.00000000.00000000.00000001 Network Address: 1.0.0.0 00000001.00000000.00000000.00000000 Broadcast Address: 1.255.255.255 00000001.11111111.11111111.11111111
Adam’s IP Address:
IP Address: 1.0.0.2 00000001.00000000.00000000.00000010 Network Address: 1.0.0.0 00000001.00000000.00000000.00000000 Broadcast Address: 1.255.255.255 00000001.11111111.11111111.11111111
Sara’s IP Address:
IP Address: 1.0.0.3 00000001.00000000.00000000.00000011 Network Address: 1.0.0.0 00000001.00000000.00000000.00000000 Broadcast Address: 1.255.255.255 00000001.11111111.11111111.11111111
Up to the last IP Address of Network One 1.0.0.0
John’s IP Address:
IP Address: 1.255.255.254 00000001.11111111.11111111.11111110 Network Address: 1.0.0.0 00000001.00000000.00000000.00000000 Broadcast Address: 1.255.255.255 00000001.11111111.11111111.11111111
IP Addresses from Network 126.0.0.0
IP Address: 126.0.0.1 01111110.00000000.00000000.00000001 Network Address: 126.0.0.0 01111110.00000000.00000000.00000000 Broadcast Address: 126.255.255.255 01111110.11111111.11111111.11111111
Up to the last IP Address of Network 126
IP Address: 126.255.255.254 01111110.11111111.11111111.11111110 Network Address: 126.0.0.0 01111110.00000000.00000000.00000000 Broadcast Address: 126.255.255.255 01111110.11111111.11111111.11111111
Note: Network Address a.k.a Netmask Address or Subnet Mask
Next, let’s look at how Class B Networks created from the 128 remainder.
Subject Related
By Wikipedia Classful Networks | Router Ally IPv4 | HighTech IPv4 Addressing | The TCP IP Guide | Cisco CCNA Simplified | Cisco CCNA in 60 Days | CCNA R&S Certification Kit | Subnetting Made Easy | Who is Running the Internet | IP Addressing and Subnetting | The Only IP Book You Will Ever Need!
"Understanding Class A Network IP Addresses",CCNA Routing and Switching
<< IP and Network Fundamentals Course
>> IPv4 Address System Section
Thanks for the great info.
Please, may I understand why private IP address for class A networks always starts with 10. all the time?
I do understand why the public IP range starts from 1 to 126 but really confused why the private one started with 10., is it something agreed between creators of the IP or it is something calculated as we did with the public IP?
Thanks
Thanks!!! Very helpful. Broke it down real easy for me. Although i still don’t understand the reason for dividing 256 by 2.
I apologize cj for being late. Since binary is based on 2 base, therefore, we divide 256,128,64,32,16,8,4,2, and 1 by 2. Since 256 represented the whole, 2 divided the whole to 128 Networks, hence, Class A Networks created. It takes some practice to understand all linking dots. I hope that answered your question