IP Address Classes

Assigning IP Address to a class is called classful addressing.

ARIN – American Registry for Internet Numbers manages the allocation of addresses.

There are five different types of classes:

Class A:

  • Created to allow very large networks
  • The first octet is used to define the network
  • The first bit has to be: 0
  • Range: 1 – 126 (actually 0 – 127, but 0 and 127 are reserved for other purposes)

Class B:

  • Created for medium sized networks
  • Uses the first two octets to define the network
  • The first two bits have to be: 10
  • Range: 128 – 191

Class C:

  • Created for many small networks
  • Uses the first three octets to define the network
  • The first three bits have to be: 110
  • Range: 192 – 223

Class D:

  • Created for multicasting
  • The first four bits have to be: 1110
  • Range: 224 – 239

Class E:

  • Reserved for the Internet Engineering task force (IETF)
  • First four bits have to be 1111
  • None of these addresses have been released for use on the internet
  • Range: 240 – 255

Related Topics:

CCNA Study Guide – The fastest way to get Cisco Certified Guaranteed!
Learn to Subnet – The Complete Guide to Mastering How to Subnet
ICND1 Study Guide – Contains everything you need to know to get your CCENT Guaranteed!

Category: CCNA Study Guide, ICND1 Study Guide, IP Address | Tags: , , , , , , , 6 comments »

6 Responses to “IP Address Classes”

  1. gaurav
    July 5th, 2010 at 11:00 pm

    why do we need to define IP classes ???
  2. blake
    July 6th, 2010 at 7:26 am

    That is a very good question gaurav! IP Address Classes were created originally to make sure IP address were allocated in an efficient manner. This was before subnetting was used. If there was a really large ISP they could get a large class A so that they would have enough IP Addresses to give out. If you were a business you would be assigned a class C. Routing protocols like RIPv1 rely on these IP classes instead of subnet’s.
  3. Ajay Kumar
    July 14th, 2010 at 10:54 am

    my question from class A:
    “The first bit has to be: 0″ why it is taken as 0?
    &
    “0 and 127 are reserved for other purposes” what do you meant for other purposes?
    can’t understood :( please elaborate it
  4. blake
    July 20th, 2010 at 1:52 pm

    Yes the 0 and the 127 subnet are reserved for special purposes and can’t be assigned as a real world IP Address because they don’t get routed. For example the 0.0.0.0 address is used to specify the default gateway. 127.0.0.1 is used as the localhost address on every single computer. You can even ping 127.0.0.1 and your computer will respond back.
  5. Ajay Kumar
    August 1st, 2010 at 2:52 am

    oh thannx blake; my path director….i like the way You* replied back to me :)
    i’m also like the way You* smile :)
    one more time thanxx :) i hope in future you’ll again help me…
  6. blake
    August 1st, 2010 at 11:52 pm

    No problem Ajay, I’m here to help. Let me know if you have anymore questions about anything else.

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