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Unit 10: Network Layer in the Internet

and maintaining one server sun out of many servers, which is linked to Internet through its web Notes
server. Likewise any organization with several departments may create addresses for its sub
domain with different servers being maintained there.
Internet is the collection of several independent networks, which are interconnected with one
another. Now each independent network may have several hosts. Keeping this in mind, you can
now think of address of your house. Your house has a unique house number, which is not
assigned, to any other house in your locality. In this case, your house can be considered as a host.
Your locality can be considered as network and your city as domain. You can write your address
in Internet addressing notation as houseno.locality.city. If suppose you want to tell your address
to a foreigner, then you will have to add your country name in your address. In this case it will
become houseno.locality.city.country. Now if anybody desires to send you a letter or visit your
house, he will first has to come to your country and then to your city. After that he will reach to
your locality and then your house by your house number. The same analogy applies in case of
Internet addressing.
We have already noted that a host on Internet has two parts. These are identification of the
network and identification of the host on the network. In this manner, the address of a host is
therefore comprised of two parts namely network address and host address. These two parts
together make 32 bit long IP address for a particular host on the Internet. The IP address, which
will see in the subsequent discussion, is written in four octets each separated by a dot. It may
have a form like 197.23.207.10.

Notes Presently, we are using IP address version 4 (IPv4). However, IP address version 6
(IPv6) is gradually under implementation stage.

10.1.2 IPv4 Addressing

IPv4 addresses are uniquely used as identifiers, which work at network layer to identify the
source or destination of IP packets. Presently, the version of IP, which is in use, is called as IPv4.
In this version, every node on Internet may have one or more interfaces, and we are required to
identify each of these devices with a unique address assigned to each of them. It means that each
node is assigned one or more IP addresses to invoke TCP/IP. These are logical addresses and
have 32 bits.
Technically, IP addresses are expressed using binary notation with 32 bit long string. In order to
make these strings to remember easily, dotted decimal notations are used, in which periods or
dots separate four decimal numbers from 0 to 255 representing 32 bits. As there are 32 bits
therefore each decimal number contains 8 bits and called octet.
For example, the IPv4 address 11000000101010000000101000011001 is expressed as 192.168.10.25
in dotted decimal notation. Below are the steps to convert an IPv4 address from binary notation
to dotted decimal notation:
 Break 32 bit long address into segments of 8-bit blocks: 11000000 10101000 00001010 00011001

 Write decimal equivalent of each segment: 192 168 10 25
 Separate the blocks with periods: 192.168.10.25
Figure 10.2 shows the IP address structure.

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