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Remember IP address Classs, Private Address Space and Default Subnet Masks

Updated on July 5, 2011

I always mention to memorize IP address Classes, Private Address Space and Default Subnet Masks. You must have to remember them. Without remembering them it's quite harder to find out the answers related to IP addressing and subnetting. I think you are already familiar the necessity of learning IP addressing and subnetting. Any CCNA exam or job exam or interview exam, must set some of the questions. So, I'm telling you seriously, to be the boss of IP addressing and subnetting, you must have to remember the class of IP addresses, private address space and default subnet masks. These are never changing. So, memorize them. This page only contains IP address classes, private address space and default subnet masks. The only things you need to remember is mentioned this page.

[Note: Visit Subnetting Index or type to your browser address bar to learn a-to-z of subnetting. Many examples are there to make you a smart master of subnetting.]

IP Address Classes

Each IP address has 32 bits (in IPv4). These 32 bits are divided into 4 blocks. Each block is separated by a dot (.). IP address can be classified into five classes. They are defined as Class A, Class B, Class C, Class D and Class E. Remember the following chart:

Class Name     Range
Class A          1-127
Class B        128-191
Class C        192-223
Class D        224-239
Class E        240-255


  • Class D is reserved for multicast purposes.
  • Class E addresses are reserved for experimental purpose only or for future research purposes.

Private Address Space

The following private address space you need to remember:

Class Name     Address Space Range
Class A      to
Class B    to
Class C   to

Default Subnet Mask

The following default subnet mask you need to remember:

Class Name     Default Subnet Masks
Class A
Class B
Class C

Please memorize the above IP address classes and their ranges, Private IP address space and Default subnet masks. They are very necessary when you will do subnetting and address calculating. So, memorize them all.

© Written by rancidTaste


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    • profile image

      oshinkoya babatunde 

      6 years ago

      pls, i want to know why ip addresses are grouped into five classes. what is the significance of this

    • profile image


      6 years ago

      class a subnet masks how to use

    • profile image

      Binish Baby 

      8 years ago



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