[adeel420] IP ADDRESSES
- From: "Sajid Iqbal" <sajid_cyberspace@xxxxxxxxxx>
- To: <"Undisclosed-Recipient:;"@smtp-2.hotpop.com>
- Date: Wed, 11 Dec 2002 02:29:31 +0500
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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