[adeel420] IP ADDRESSES

Look around and check how many of your computer literate friends or colleagues 
have access to Internet. The answer may be 80 percent; 90 percent or even 
hundred percent. Once again see as to how many of them are familiar with the 
term IP Address. You will find that 50 to 60 percent of them know what does the 
abbreviation stand for. However, only a few of them thoroughly understand the 
structure of an IP Address, whereas to many of them the term is still alien. If 
it's alien for you too, read this brief tutorial.
Also called as Internet Address it's used to identify each host on a network 
running TCP/IP transport. To start with, always remember that an IP Address is 
a 32 bit number. It comprises four values separated by periods. Each value 
represents a Byte therefore it may range from 0 to 255. Therefore, (0.0.0.0) is 
the lowest and (255.255.255.255) is the highest possible IP address.

Reading the above you may get the impression that any combination of numbers 
from the mentioned can be assigned to a device within a network. Not at all; 
each bit of this combination of 4 Bytes has a certain interpretation. To decode 
an IP address, let's try to understand its different classes.

An IP address is divided into 2 sections as given below:

i. Network number (to which the IP address is assigned)

ii. The remainder is the host number that identifies a specific host on the 
network.

Remember that the term Host used in this article is entirely different when 
compared with the Host of conventional computing environment, where the Host is 
a large central computer. In context of Internet, it could be any device that's 
assigned unique address and is individually accessible. It's also referred to 
as a node. Internet Host can be a PC, an individual router port, or even a 
communications link between two networks.

InterNIC has classified the network address into 5 different classes i.e. A, C, 
D, E and F. D and E are not commonly used.

Class A

This type uses only first Byte for a network address, leaving other 3 Bytes for 
the host address. However, in Class A type of IP Addresses only 126 addresses 
are available for the network. Number of available hosts for each class A 
network is 16,777 in a Class A network. This class is meant for huge 
organizations.

Class B

In this type first two bytes are used to assign the number for the network, and 
the remaining 2 bytes are left for identifying the host on each network of such 
type. This class is mainly booked for very large companies and ISPs.

Class C

First three Bytes in this type are used to represent network address leaving 
only one Byte for hosts on this type of networks. This type is typically 
assigned to small companies. Mathematically, for Class network addresses 
16,777, 214 are available, and the numbers reserved for hosts per network of 
this type is 254.

Therefore, try to remember the rule that in order to be accessible on a TCP/IP 
network a device must be assigned an IP Address.

I hope you have conceived what has been explained above. However, it may still 
be difficult for you to recognize the type of a given network address. To 
determine its type, let me be more precise. See the left most 3 bits of the 
first Byte of any IP Address. The pattern for eight bits of the first Byte for 
a Class A address is (0 XX). To make it more clear see below:

0 1 1 1 1 1 1 1

128 64 32 16 8 4 2 1

Thus, the first bit of the left most Byte in a Class A network address will 
always be zero as described by the pattern (0XX). Here 'X' represents: either a 
0 of 1. SO, the first bit mentioned in the example is 0; we have to ignore 128. 
Add the remaining values as:

64+32+16+8+4+2+1=127.

So, the highest possible value is the total as 127. Once again it's emphasized 
that the first Byte of Class A network must begin with OXX pattern where first 
Byte is zero and X represents either O (zero) or 1.

In a Class B network address the initial most 3 bits of the leftmost Byte have 
the pattern as 10X, where X represents either a 0 (zero) or 1.

1 0 1 1 1 1 1 1

128 64 32 16 8 4 2 1

Therefore, the highest possible number as worked out by following the bit 
pattern (10X) is 191. The 0 (zero) bit has been ignored which is 64 in this 
example.

Refer to Class A network again where it ends at 127. So, any IP addresses 
beginning from 128.1.0.0 to 191.254.0.0.0 is a Class B network Address. 
Similarly in a Class C network address the initial 3 bits of the first Byte are 
of the pattern (110) represented as follows

1 1 0 1 1 1 1 1

128 64 32 16 8 4 2 1

Adding (128, 64,16,8,4,2,1) we get 223. According to the mentioned pattern the 
0 (zero) bit -- 32 in this case has been ignored. Remember class C networks can 
be as high as 223 maximum. Therefore, any network address (IP address) ranging 
from 192.0.1.0 to 223.255.254.0 must be a class C network address.

TCP/IP is too detailed a topic to be covered by this brief tutorial. It needs 
numerous other sessions to be understood thoroughly. Therefore, wait until the 
next issue for more detailed discussions.

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