this lesson will guide you to know about IP address of computer.

1. 1/19/2015 What is the IP Address?
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The IP Address
Every computer on a network and the internet needs an address. This address is known as an IP address.
Two computers can never have the same address. An IP Address is a group of 4 eight bit binary numbers
represented in decimal. Each number is separated by a period, e.g. 10.1.0.1. Any machines that are
connected to a network will each need a unique address. Two machines cannot use the same address.
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The IP address is divided into the network ID and
the host ID. The network ID represents what
network the machine is on. For two machines to
communicate they have to be using the same
network ID. The host ID represents a unique number
assigned to the machine attached to the end of the
network ID. For two machines to communicate they
need to Have the same network address. They
must, however have different host numbers.
A machine can identify which part of its IP address
is the host ID and which part is the network ID by
using a set of numbers called a subnet mask.

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Subnet Masks
As well as an IP address every machine using TCP/IP needs a subnet mask. The subnet mask splits the
IP address into two parts, allowing the computer to identify which part is the network ID and which part is
the host ID.
The subnet mask divides the IP address into two parts by using on (1) and off (0) switches. 1 represents a
network ID and 0 represents a host ID.
A computer with an IP address of 10.1.0.1 and a subnet mask of 255.255.0.0 would have a network ID of
10.1 and a host ID of 0.1. This is worked out by converting both numbers into binary.
10 .1 .0. 1
00001010.00000001.00000000.00000001
255 .255. 0. 0
11111111.11111111.00000000.00000000
Using the subnet mask, divide the IP address up by using the 1’s to represent the network ID and the 0’s to
represent the host ID.
00001010.00000001.00000000.00000001
11111111.11111111.00000000.00000000.
Using this, we can assume that the network ID is 00001010.00000001 (10.1) and the host ID is
00000000.00000001 (0.1).
A subnet mask doesn’t have to be a full octet. It is possible to use a subnet mask that is only a partial octet.
For example 255.255.240.0: This enables the administrator to create custom subnets to divide a private
network into several discrete sub­ networks
Bit Notation
An easier way of writing an IP address and its subnet mask is by using the form xxx.xxx.xxx.xxx/bits in the
mask. The address 10.1.0.1 with a subnet mask of 255.255.0.0 can also be written as 10.1.0.1/16.
This form of notation shows the number of Bits in the subnet mask, e.g. /8 represents
11111111.00000000.00000000.00000000 or 255.0.0.0.
/20 would represent 11111111.11111111.11110000.00000000 or 255.255.240.0.
IP Address Classes
When TCP/IP first appeared, IP addresses were placed into different classes A,B,C and D. The subnet
mask of the machine would be determined by its IP address class. To determine what class an IP address
is , refer to the first octet of the address, e.g. 100 for 100.23.23.1
To determine what class an IP address is , refer to the first octet of the address, e.g. 100 for 100.23.23.1

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Class Subnet Mask Host ID’s
A 255.0.0.0 16,777,214
B 255.255.0.0 65,534
C 255.255.255.0 254
D 255.255.255.255 (Multicast) N/A
Of the 32 bits available, the bits required for the
network ID can’t be used. In a class B network for
example this takes away 16 bits, leaving 16 bits for
the host addresses. This can be used to make
numbers up to 65536 (2 to the power 16). Host
addresses using all 1’s or all 0’s are reserved for
special use, hence the figure in the above table of 65534.
You have been assigned the address 134.34.0.0/20, how many hosts will you have?
/20 represents the subnet mask of 11111111.11111111.11110000.00000000 (255.255.240.0)
Therefore the Host ID is 0000.00000000, giving a total of 12 host ID’s to play with.
Therefore (212)­2=4094. So there are 4092 different host ID’s
Why take off 2?
Two host ID addresses are reserved for every network.
If the host ID contains all 0’s it represents the Network it is on and can’t be used, e.g. 10.1.0.0/24
(00000000) is invalid. This is known as the Network Address.
If the host ID contains all 1’s then this represents every computer in the network. This is known as the
Broadcast Address, e.g. 194.34.23.255/24 (11111111) represents every computer in the 194.34.23 network.
Reserved addresses:
If the host part of the address is all zeroes, this looks similar to the subnet mask and is called the Network
Address. By convention, this address is not used for any host. If the host part of the address is all ones, this
represents not a single host but all hosts on that network. It is termed the broadcast address, and it shouldn’t
be used for any host.
Although these days you can have any subnet mask, classes are still used when a subnet mask isn’t given.
There are a number of private address ranges available for use in internal networks. These addresses will
never be seen on the internet. As internet routers will not pass packets that originate from these addresses.
Class A : 10.0.0.0 – 10.255.255.255
Class B : 172.16.0.0 – 172.31.255.255
Class C : 192.168.0.0 – 192.168.255.255
Custom Subnet Masks
Imagine a scenario where you have been assigned the address range 193.28.34.0 for your company’s
network. You need to have 14 separate networks each with ten computers in.
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Comments
The IP Address — 29 Comments
193.28.34.0 is a class C address which means you have 254 hosts but only the one network (the 193.28.34)
network.
Considering that you only need 10 hosts and not 254 we can take some of the host ID’s and turn them into
Network ID’s. You can do that by creating a custom subnet mask…
We have the 8 host digits to play with. This equates to (28)­2=254 addresses. However we only need 140.
Some of the host ID’s can be used as network ID’s.
Routers
Routers are network devices that are used to connect separate networks and to enable network traffic to
pass between the networks. We have seen that machines on separate networks cannot pass data between
themselves without assistance. A router or default gateway passes data to addresses that are not on the
senders network.
With the help of a router computers on both networks would be able to communicate. The router is physically
connected to both networks and has two IP addresses.
When a client wants to send a packet out on the network it checks the network ID of the destination
machine. If it is different from its own it would send the packet to its default gateway.
Routers can communicate with other routers so that network packets can be passed to their correct
destinations.
A network packet travelling out on the internet may pass through several routers before reaching its target.
Each router forwards the packet on to the next router until it either reaches or fails to reach its destination.
Routing is covered in much greater detail later on in this course.
Modeste
on January 8, 2015 at 8:59 am said:
There is an error to be rectified. A ntwk with the subnet mask of /20 can host 2^12­2=4094 computers
instead of 4092. Am I wrong?
souransu mukherjee
on January 2, 2015 at 2:28 pm said:

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THANKS A LOT FOR THE ARCHITECTURE,BUT WE ARE WAITING FOR DETAILS OF ROUTER
REGARDS
Paul Tagau
on December 29, 2014 at 4:42 pm said:
Very interesting course. I like it please enrole me to the next lesson.
elvis mwape
on December 28, 2014 at 12:02 am said:
It a nice and very helpful lesson.
Am lost on how to find host I’d. Can u pliz help me
okunlola samuel olugbenga
on December 24, 2014 at 6:55 am said:
thanks
ATIF
on December 17, 2014 at 1:30 pm said:
HI! I dont understand questions no 7,8,10.
Sarath
on December 8, 2014 at 8:56 am said:
Simple and clear lesson