Understanding Class A Network IP Addresses

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.

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.

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