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Difference Between Class C & Class D IP Addresses

11/22/2011 02:38 by LindaRodrigues

First answer posted by lainib at 11/22/2011 02:38
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  • lainib
  • Those who have seen an IP address will remember that it is shown as four numbers each separated by a dot ("."). This is just a way of representing the true address in a form easier for humans to copy. The real address is a 32-digit binary number in the original scheme of the IP address. The address was divided into two parts, a network ID and a host ID. The size of each part varied depending on the class of the address. Class C and Class D are two of the categories explaining where the division of the IP address lies.


    Classful Addressing

    In Classful Addressing, the first part of the IP address is the network ID and the second part is the host ID. Each part takes up a different amount of numbers depending on the class. Class C addresses give the first 24 positions to the network ID and leave eight positions for the host ID. The network ID identifies the network to the outside world. The host ID is a specific computer within that network. Classes A, B and C are allocated to: large networks with many computers (Class A), mid-sized networks (Class B) and small networks with few computers (Class C). Class D addresses are not divided between network ID and host ID. The entire space is used to identify a multicast group. Classes A, B and C enable one-to-one communication, while Class D enables one-to-many communication.


    Class Identification

    Although the first segment of the IP address in Classes A, B and C identifies the network ID, the first four bits actually identify the class. If the first bit is a zero, the address is Class A, if the address starts with "10" it is Class B. Class C addresses all begin with "110"and Class D addresses begin with "1110." This leaves Class E with all addresses starting with "1111." Half of all IP addresses under this scheme are Class A addresses, a quarter of all addresses are Class B, an eighth of all addresses are Class C, and Class D and Class E each have one-sixteenth of all addresses. Class E addresses are reserved for research. This scheme classifies all addresses between and as Class C and all addresses between and as Class D.



    Class D addresses operate differently from the conventional usage of Classes A to C. A multicast is like an opt-in mailing list. Each IP address references a group. Any computer wishing to be a part of that group sends a registration message to that IP address. Any data message sent to that IP address is forwarded to all the IP addresses registered in that group.


    Classless Addressing

    Classful Addressing wasted a lot of addresses. It kept half of all IP addresses reserved for large companies, when the uptake of the Internet by the general public created large demand for Class C addresses. The class system was scrapped in 1993 with the introduction of "Classless" IP addresses. This effectively merges Classes A, B and C, although the Class D range of addresses for IP multicasting still exists.

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