Why ip addresses has been divided into 3 classes

A 0-127
B 128 -191
C 192-255

What is the use of it?


And plz. tell me what is the difference b/w TCP and UDP protocols?

Ip addressing is 5 classes not 3 classes. These classifications are done only based upon the value in MSB(Most significant bit).
0 = Class A
10 = Class B
110 = Class C
1110 = Class D/Multicast
1111 = Reserved

Now why only these classes.? It is incepted in 1970s. and it is well designed. They thought the no of hosts in and no of networks are suffiecient .Thy ar order of 2 power 24 hosts in class A and 2 power 8 hosts in Class C. But as the Internet evolved from 1970s now the poeple want to address the problems in Ipv4 hence came IPnex, Ipv5, IPv6 etc....

soma sekhar

The A,B,C classes are divided by host and network divisions when looking at the IP address
Also helps determine the default subnet mask.

Class A
103 . 205 . 7 . 16
Host | Network address


Class B
153 . 65 . 137 . 201
Host ----- | Network address


Class C
201 . 121 . 37 . 5
Host ----------- | Network address
----------------------------------------------------------------------------------------------------
Transmission Control Protocol
User Datagram Protocol

TCP is a guarenteed delivery of data, UDP does not guarentee you get the whole message. Since most of us want the whole thing we download, we use TCP that is sent across IP. In some cases though you are actually using UDP/IP. If you watched a streaming video, the server streaming it to you is constantly sending more data. It doesn't care about delivery because it needs to keep the continuous stream moving. If by chance a packet is missed along the way to you, your video file might jar or skip a bit but picks right back up.

For more, you should probably check out learntosubnet.com and grab the TCP/IP bible.

Basically IP was setup into the different classes because it was a more efficient use of the ip addresses. Class A Networks could be assigned to the govt and large corporations who require numerous hosts. Class B could be assigned to smaller corporations, and companys like ISP's, class A's are assigned to ISP's as well. Class C is assigned to small companys and small ISP's. THen there are the two restricted Classes for research and such. THen there is the matter of the reserved A, B, and C classes for internal use. That also allows internal networks to share a single or a few Public IP's. FOr instance when you run masquerade on linux, or buy a router at the store, they perform NAT and allow you to have multiple computers inside the firewall sharing one public IP.

ALex