[Complete Guide] Class A IP Address, Subnet Mask, and Subnetting

By | September 5, 2013
SmartPCTricks is now going to introduce networking classes online…! This is the first tutorial among them dealing with classes of IP address.
Every device running on the internet has been assigned an unique address (number) called IP address. Without IP address your device become isolated from the network and you will not be able to communicate with other network devices.
IP address is just like telephone numbers each one being unique and used to find a way to reach you and only you…!.
If you are working on a networking related stream it is very important that you should have basic knowledge about the architecture and structure of IP address.

This article deals with IP address classes and subnet mask with special focus on class A.
There are two versions of IP addresses: IPv4 and IPv6 addresses.
IP V4 uses 32-bit addresses and has 4,294,967,296 possible unique addresses.
  • Due to the fast growth of the Internet there are chances of IP address getting exhausted in the near future.
  • To overcome this issue IP V6 has been introduced which is a 128-bit address. IP V6 is not under the scope of this article, hence we will discuss it later.
  • IANA (Internet Assigned Numbers Authority) is the organization under the Internet Architecture Board (IAB) of the Internet Society that,under a contract from the U.S. government has overseen the allocation of Internet Protocol addresses to Internet service providers (ISPs).

What is subnet mask?

As the name indicates, Subnet mask subdivides a larger network into smaller networks. Without subnet mask all the computers in the internet may communicate each other without any control..! It is crazy….
So how to make communication control between network devices?
Here comes the importance of subnet mask and IP classes.
The total available IP address is divided into different classes according to the value in 1st octet and subnet mask in order to make unique  networks.
Typically the range of IP address starts from 0.0.0.0 to 255.255.255.255, thus for proper management of these IPs Subnet mask has been introduced.
In IP V4 addressing strategy, according to the subnet masks we can find 5 IP classes:
  1. Class A
  2. Class B
  3. Class C
  4. Class D
  5. Class E
As IPv4 is still the widely used protocol, this tutorial will be focusing on Class A IP version 4 addressing and subnetting.

Format of Class A IP Address

An IP V4 address involves 4 numbers separated by periods, the numbers taking a possible range of 0 through 255 as the least number that is possible using 8 bit is 0 and the large number using 8 bit is 255.
Each group or octet consisting of 8 bits.
A typical IP address has two parts namely ‘Network part’ and ‘Host Part
For Class A IP address, 1st octet represents the Network part and rest all octets indicates host (devices) in the network.
The default subnet mask of class A network is 255.0.0.0
Thus it is possible to connect 224 network devices per network. Thus class A is used for very large network.

Range of Class A IP address

  • IANA (Internet Assigned Number Authority) configured IP class A as Public and Private.
Following table show the Class A IPs
  • Basically class A IP starts from 1.0.0.0 to 127.255.255.255.
  • In this range the network 10.0.0.0 is dedicated for use in Private network. For example if you have an office you can configure the network devices with IP starting from 10.0.0.1 to 10.255.255.254 only.
  • All other IPs are held at service provides, only we can do is purchase it from them.
You may wonder about why we are not using 10.0.0.0 and 10.255.255.255?
The IP 10.0.0.0 is used to indicate the Network itself while routing and 10.255.255.255 is termed as Broadcast address. Both of these are used while routing.

What is the use of 0.0.0.0 IP Address

  • In the Internet Protocol version 4 the address 0.0.0.0 is a non-routable meta-address used to label an invalid, unknown or non-applicable target.
  • Having this address, a computer cannot be connected or communicated with any other devices over IP. TCP/IP software applications also use 0.0.0.0 as an encoding technique to observe network traffic from any valid IP address.
  • 0.0.0.0 can be seen initially as a default IP address. It is the IP that is used by a computer that DHCP allocation fails, but it is associated with a network.

What is the use of 127.0.0.0

  • Network 127.0.0.0 (means 127.0.0.1 to 127.255.255.254) is reserved as Loop back address.
  • This permits you to develop and examine networking software without ever using a “real” network.
  • It is used for self pinging, just try to ping 127.0.0.1 from your PC, you will get reply.

Breakdown each part of IP

Here I’m going too deep inside the class A IP address. The starting IP address of all network, that means __.0.0.0, is used for representing the network itself. It often used while routing.Also the last IP address in a network that is __.255.255.255 is termed as Broadcast address.

Only the remaining IP address are available for assigning clients.

So in class A, it is possible to create 126 networks each having
224-2=16777214 clients maximum. Since 2 IPs are Network address and broadcast address.

How to Identify Whether The IP Address Belongs to Class A?

On the first sight we can say that the given IP address belongs to which class. For this, take a look at the network bits (1st octet), if the 1st bit is ‘0’, then the IP comes under the Class A.

Identify Class of IP Address

1st bit is always ‘0’ in the range of 0 to 127 if we are writing in 8 bits. Thus it is very easy to identify given IP goes to Class A or not.

Class A IP Address Subnetting

As we already discussed subnetting gives multiple networks, Obviously default subnetting cause classes in IP addresses.Here I planned to give you a subnetting tutorial about class A subnetting. The default subnet mask of class A IP is 255.0.0.0, even though we can create manual subnets for effective management of IPs.

For example there is only one network possible for the range of IPs from 10.0.0.0 to 10.255.255.255.

Using manual subnetting we can do multiple networks using the same range of IPs.

How to do subnetting for class A? Below I’m discussing subnetting in detail.

Class A One Bit subnetting

For example I took private network range, the default configuration isIP,                 :-  10.0.0.0    –    00001010 00000000 00000000 00000000
Subnet Mask  :- 255.0.0.0  –    11111111 00000000 00000000 00000000NB:- Underline part shows Network bits

Now I’m taking 1 more bit from host part of subnet mask to network part, then the binary configuration of subnet mask should be,

11111111 1 0000000 00000000 00000000    –   255.128.0.0

Thus we have 223 = 8388608 host per network.

The total default class A network with 224 IPs gets divided in to two different networks each having 223 = 8388608 IPs.

Here we have 7 host bits in 2nd octet since the 1st bit we had already taken for network part, the maximum possible number using 7 digit is 1111111 = 127. Thus above 127, we may get another network.

The number of subnets is calculated by 2n, where n is the extra additional bit taken for subnetting.
Thus for 1 bit subnetting. n = 1 so 2= 2 subnetworks are possible.

1 bit subnetting can also be represented as [Network address] /9
where 9 is the number of network bits.

Below table shows all possible IPs with 1 bit subnetting on Class A private range.

Similarly subnetting can be done on 1.0.0.0, 2.0.0.0, ……. , 9.0.0.0 and 11.0.0.0, 12.0.0.0, ….. , 126.0.0.0 networks also.

Class A Two Bit Subnetting

One bit subnetting gives two networks and here two bit subnetting gives 4 networks.So for n=2,  22=4 sub networks are possible. Each network having 222 = 4194304 IPs, among these 4194302 IPs are usable.

For 2 bit subnetting the subnet mask should be
11111111 . 11 000000 . 00000000 . 00000000 = 255.192.0.0

Also represented as [Network address] /10 
where 10 is the number of network bits.

Below table shows all possible IPs with 2 bit subnetting on Class A private range.

Similarly subnetting can be done on 1.0.0.0, 2.0.0.0, ……. , 9.0.0.0 and 11.0.0.0, 12.0.0.0, ….. , 126.0.0.0 networks also.

Class A Three Bit Subnetting

Three bit subnetting gives 23= 8 sub networks.
Each network having 221 = 2097152 IPs, among these 2097150 IPs are usable.For 3 bit subnetting the subnet mask should be
11111111 . 111 00000 . 00000000 . 00000000 = 255.224.0.0
Also represented as [Network address] /11 
where 11 is the number of network bits.
Below table shows all possible IPs with 3 bit subnetting on Class A private range.

Similarly subnetting can be done on 1.0.0.0, 2.0.0.0, ……. , 9.0.0.0 and 11.0.0.0, 12.0.0.0, ….. , 126.0.0.0 networks also.

Class A Four Bit Subnetting

Four bit subnetting gives 24= 16 sub networks. Each network having 220 = 1048576 IPs, among these 1048574 IPs are usable.For 4 bit subnetting the subnet mask should be
11111111 . 1111 0000 . 00000000 . 00000000 = 255.240.0.0Also represented as [Network address] /12
Where 12 is the number of network bits.

Below table shows all possible IPs with 4 bit subnetting on Class A private range.

Similarly subnetting can be done on 1.0.0.0, 2.0.0.0, ……. , 9.0.0.0 and 11.0.0.0, 12.0.0.0, ….. , 126.0.0.0 networks also.

Class A Five Bit Subnetting

Five bit subnetting gives 25= 32 sub networks. Each network having 219 = 524288 IPs, among these 524286 IPs are usable.For 5 bit subnetting the subnet mask should be
11111111 . 11111 000 . 00000000 . 00000000 = 255.248.0.0Also represented as [Network address] /13 where 13 is the number of network bits.

Below table shows all possible IPs with 5 bit subnetting on Class A private range.

Similarly subnetting can be done on 1.0.0.0, 2.0.0.0, ……. , 9.0.0.0 and 11.0.0.0, 12.0.0.0, ….. , 126.0.0.0 networks also.

Class A Six Bit Subnetting

Six bit subnetting gives 26= 64 sub networks. Each network having 218 = 262144 IPs, among these 262142 IPs are usable.For 6 bit subnetting the subnet mask should be
11111111 . 111111 00 . 00000000 . 00000000 = 255.252.0.0Also represented as [Network address] /14
Where 14 is the number of network bits.

Below table shows all possible IPs with 6 bit subnetting on Class A private range.

Similarly subnetting can be done on 1.0.0.0, 2.0.0.0, ……. , 9.0.0.0 and 11.0.0.0, 12.0.0.0, ….. , 126.0.0.0 networks also.

Class A Seven Bit Subnetting

Seven bit subnetting gives 27= 128 sub networks. Each network having 217 = 262144 IPs, among these 262142 IPs are usable.For 7 bit subnetting the subnet mask should be
11111111 . 1111111 0 . 00000000 . 00000000 = 255.254.0.0Also represented as [Network address] /15
Where 15 is the number of network bits.

Below table shows all possible IPs with 7 bit subnetting on Class A private range.

Similarly subnetting can be done on 1.0.0.0, 2.0.0.0, ……. , 9.0.0.0 and 11.0.0.0, 12.0.0.0, ….. , 126.0.0.0 networks also.

Class A 8 bit Subnetting, possible?

While we go for 8 bit subnetting, the network changes to class B.8 Bit subnetting of class A means there are 16 bits of network bits, this is the same as Blass B.
Class B default subnet mask is 255.255.0.0 Thus subnetting is possible up to 7 bits only.At last we have covered everything related to subnetting class A IP address.

Next Class B IP Address, Subnet Mask, and Subnetting

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