This document provides an overview of internetworking and routing concepts. It defines internetworking as connecting two or more computer networks using devices like routers and a common addressing scheme. The three main types of internetworks are extranets, intranets, and the public Internet. IP is the common protocol used for internetworking and routing. IP packets contain source and destination addresses and are forwarded through routers using routing protocols. Performance factors like delay, throughput and packet loss are also discussed.

1. UNIT-III INTERNETWORKING &
ROUTING
Basic Internetworking –IP- What Is an
Internetwork? - Service Model - Global
Addresses - Datagram Forwarding in IP -
Subnetting and Classless Addressing- ARP-
DHCP-ICMP- Routing – RIP- OSPF- Global
Routing-Interdomain Routing(BGP)- IPV6-
Multicast Routing- DVMRP.

2. Basic Internetworking
• Internetworking started as a way to connect disparate types
of computer networking technology. Computer network term is used
to describe two or more computers that are linked to each other.
When two or more computer LANs or WANs or computer network
segments are connected using devices such as a router and configure
by logical addressing scheme with a protocol such as IP, then it is
called as computer internetworking.
• Internetworking is a term used by Cisco. Any interconnection
among or between public, private, commercial, industrial, or
governmental computer networks may also be defined as an
internetwork or “Internetworking“.

3. Basic Internetworking
•In modern practice, the interconnected computer networks
or Internetworking use the Internet Protocol. Two architectural
models are commonly used to describe the protocols and methods
used in internetworking. The standard reference model
for internetworking is Open Systems Interconnection (OSI).

4. Type of Internetworking
Internetworking is implemented in Layer 3
(Network Layer) of this model The most notable
example of internetworking is
the Internet (capitalized). There are three variants
of internetwork or Internetworking, depending
on who administers and who participates in them
•Extranet
•Intranet
•Internet

5. Extranet
 An extranet is a network of internetwork or Internetworking that
is limited in scope to a single organisation or entity but which also
has limited connections to the networks of one or more other
usually, but not necessarily, trusted organizations or entities.
 Technically, an extranet may also be categorized as a MAN,
WAN, or other type of network, although, by definition, an extranet
cannot consist of a single LAN; it must have at least one connection
with an external network.

6. Intranet
 An intranet is a set of interconnected networks or Internetworking, using
the Internet Protocol and uses IP-based tools such as web browsers and ftp
tools, that is under the control of a single administrative entity.
 That administrative entity closes the intranet to the rest of the world, and
allows only specific users.
 Most commonly, an intranet is the internal network of a company or other
enterprise.
 A large intranet will typically have its own web server to provide users with
browseable information.

7. Internet
 A specific Internetworking, consisting of a worldwide
interconnection of governmental, academic, public, and private
networks based upon the Advanced Research Projects Agency
Network (ARPANET) developed by ARPA of the U.S.
 Department of Defense also home to the World Wide Web
(WWW) and referred to as the ‘Internet‘ with a capital ‘I’ to
distinguish it from other generic internetworks.
 Participants in the Internet, or their service providers, use IP
Addresses obtained from address registries that control assignments.

8. IP
•IP stands for internet protocol. It is a protocol defined in the TCP/IP model
used for sending the packets from source to destination. The main task of IP is
to deliver the packets from source to the destination based on the IP addresses
available in the packet headers. IP defines the packet structure that hides the
data which is to be delivered as well as the addressing method that labels the
datagram with a source and destination information.
•An IP protocol provides the connectionless service, which is accompanied by
two transport protocols, i.e., TCP/IP and UDP/IP, so internet protocol is also
known as TCP/IP or UDP/IP.
•The first version of IP (Internet Protocol) was IPv4. After IPv4, IPv6 came
into the market, which has been increasingly used on the public internet since
2006.

9. Function
The main function of the internet protocol is to provide
addressing to the hosts, encapsulating the data into a packet
structure, and routing the data from source to the destination
across one or more IP networks.
 In order to achieve these functionalities, internet protocol
provides two major things which are given below.
An internet protocol defines two things:
•Format of IP packet
•IP Addressing system

10. What is an IP packet?
• Before an IP packet is sent over the network, two major components are added in an
IP packet, i.e., header and a payload.
• An IP header contains lots of information about the IP packet which includes:
• Source IP address: The source is the one who is sending the data.
• Destination IP address: The destination is a host that receives the data from the
sender.
• Header length
• Packet length
• TTL (Time to Live): The number of hops occurs before the packet gets discarded.
• Transport protocol: The transport protocol used by the internet protocol, either it
can be TCP or UDP.
• There is a total of 14 fields exist in the IP header, and one of them is optional.
• Payload: Payload is the data that is to be transported.

11. How does the IP routing perform?
• IP routing is a process of determining the path for data so that it can travel from the source to
the destination.
• As we know that the data is divided into multiple packets, and each packet will pass through a
web of the router until it reaches the final destination.
• The path that the data packet follows is determined by the routing algorithm.
• The routing algorithm considers various factors like the size of the packet and its header to
determine the efficient route for the data from the source to the destination.
• When the data packet reaches some router, then the source address and destination address are
used with a routing table to determine the next hop's address.
• This process goes on until it reaches the destination.
• The data is divided into multiple packets so all the packets will travel individually to reach
the destination.
• For example, when an email is sent from the email server, then the TCP layer in this email
server divides the data into multiple packets, provides numbering to these packets and
transmits them to the IP layer. This IP layer further transmits the packet to the destination
email server. On the side of the destination server, the IP layer transmits these data packets to
the TCP layer, and the TCP layer recombines these data packets into the message. The
message is sent to the email application.

12. What is IPAddressing?
An IP address is a unique identifier assigned to the computer which is connected to
the internet. Each IP address consists of a series of characters like 192.168.1.2.
Users cannot access the domain name of each website with the help of these
characters, so DNS resolvers are used that convert the human-readable domain names
into a series of characters. Each IP packet contains two addresses, i.e., the IP address of
the device, which is sending the packet, and the IP address of the device which is
receiving the packet.
Types of IP addresses
IPv4 addresses are divided into two categories:
Public address
Private address

13. Public address
The public address is also known as an external address as they are grouped under the
WAN addresses.
We can also define the public address as a way to communicate outside the network.
This address is used to access the internet.
The public address available on our computer provides the remote access to our
computer.
With the help of a public address, we can set up the home server to access the
internet. This address is generally assigned by the ISP (Internet Service Provider).
Key points related to public address are:
The scope of the public address is global, which means that we can communicate
outside the network.
This address is assigned by the ISP (Internet Service Provider).
It is not available at free of cost.
We can get the Public IP by typing on Google "What is my IP".

14. Private address
A private address is also known as an internal address, as it is grouped under the LAN addresses.
It is used to communicate within the network.
These addresses are not routed on the internet so that no traffic can come from the internet to this private
address.
The address space for the private address is allocated using Inter NIC to create our own network.
For example, a private address is assigned to the printer, which is kept inside our home, so that our family
member can take out the print from the printer.
If the computer is assigned with a private address, then the devices available within the local network can view
the computer through the private ip address.
However, the devices available outside the local network cannot view the computer through the private IP
address, but they can access the computer if they know the router's public address.
Key points related to private address are:
•Its scope is local, as we can communicate within the network only.
•It is generally used for creating a local area network.
•It is available at free of cost.
•We can get to know the private IP address by simply typing the "ipconfig" on the command prompt.

15. IP address
• An IP address consists of two parts, i.e., the
first one is a network address, and the other
one is a host address.
There are two types of IP addresses:
• IPv4
• IPv6

16. What is IPv4?
• IPv4 is a version 4 of IP. It is a current version and the most commonly used IP
address. It is a 32-bit address written in four numbers separated by 'dot', i.e.,
periods. This address is unique for each device.
For example, 66.94.29.13
• The above example represents the IP address in which each group of numbers
separated by periods is called an Octet. Each number in an octet is in the range from
0-255. This address can produce 4,294,967,296 possible unique addresses.
• In today's computer network world, computers do not understand the IP addresses
in the standard numeric format as the computers understand the numbers in binary
form only. The binary number can be either 1 or 0. The IPv4 consists of four sets,
and these sets represent the octet. The bits in each octet represent a number.
• Each bit in an octet can be either 1 or 0. If the bit the 1, then the number it
represents will count, and if the bit is 0, then the number it represents does not
count.

17. Representation of 8 Bit Octet
The above representation shows the structure of 8- bit octet.

18. Step 3: The next number is 29.

19. IPv4
Drawback of IPv4
Currently, the population of the world is 7.6 billion. Every user is having
more than one device connected with the internet, and private companies
also rely on the internet. As we know that IPv4 produces 4 billion
addresses, which are not enough for each device connected to the internet
on a planet. Although the various techniques were invented, such as
variable- length mask, network address translation, port address translation,
classes, inter-domain translation, to conserve the bandwidth of IP address
and slow down the depletion of an IP address. In these techniques, public
IP is converted into a private IP due to which the user having public IP can
also use the internet. But still, this was not so efficient, so it gave rise to the
development of the next generation of IP addresses, i.e., IPv6.

20. Introduction
to
Network
Layer
NETWORK-LAYER SERVICES
Before discussing the network layer in the Internet today, let’s briefly
discuss the network-layer services that, in general, are expected from a
network-layer protocol. Figure 18.1 shows the communication between
Alice and Bob at the network layer. This is the same scenario we used in
Chapters 3 and 9 to show the communication at the physical and the
data-link layers, respectively.

21. 18.3
Communication at the network layer
Packetizing
The first duty of the network layer is definitely packetizing: encapsulating
the payload in a network-layer packet at the source and decapsulating the
payload from the network-layer packet at the destination. In other words, one
duty of the network layer is to carry a payload from the source to the
destination without changing it or using it. The network layer is doing the
service of a carrier such as the postal office, which is responsible for
delivery of packages from a sender to a receiver without changing or using
the contents.

22. Routing and Forwarding
Other duties of the network layer, which are as important as
the first, are routing and forwarding, which are directly
related to each other.
Forwarding process

23. Other Services
Let us briefly discuss other services expected from the
network layer.
From the discussion of routing and forwarding in the
previous section, we infer that a kind of switching
occurs at the network layer. A router, in fact, is a switch
that creates a connection between an input port and an
output port (or a set of output ports), just as an electrical
switch connects the input to the output to let electricity
flow.
18.8
18-2 PACKET SWITCHING

24. 18.2.1 Datagram Approach
When the Internet started, to make it simple, the network layer
was designed to provide a connectionless service in which the
network-layer protocol treats each packet independently, with
each packet having no relationship to any other packet. The
idea was that the network layer is only responsible for
delivery of packets from the source to the destination. In this
approach, the packets in a message may or may not travel
the same path to their destination. Figure 18.3 shows the
idea..
A connectionless packet-switched network

25. Forwarding process in a router when used in a connectionless network
Virtual-Circuit Approach
In this type of service, not only must the packet contain the source and destination
addresses, it must also contain a flow label, a virtual circuit identifier that defines
the virtual path the packet should follow.

26. A virtual-circuit packet-switched network
Forwarding process in a router when used in a virtual circuit network
18.14

27. Sending request packet in a virtual-circuit network
Sending acknowledgments in a virtual-circuit network

28. Figure 18.9: Flow of one packet in an established virtual circuit
NETWORK-LAYER PERFORMANCE
The upper-layer protocols that use the service of the
network layer expect to receive an ideal service, but the
network layer is not perfect. The performance of a
network can be measured in terms of delay, throughput,
and packet loss. Congestion control is an issue that can
improve the performance.

29. Delay
All of us expect instantaneous response from a
network, but a packet,
destination, encounters
from
delays.
its source to its
The delays in a
network can be divided into four types: transmission delay,
propagation delay, processing delay, and queuing delay. Let
us first discuss each of these delay types and then show how
to calculate a packet delay from the source to the destination..
Throughput
Throughput at any point in a network is defined as the
number of bits passing through the point in a second, which
is actually the transmission rate of data at that point. In a
path from source to destination, a packet may pass through
several links (networks), each with a different transmission
rate. How, then, can we determine the throughput of the
whole path? To see the situation, assume that we have three
links, each with a different transmission rate, as shown.

30. Throughput in a path with three links in a series
A path through the Internet backbone

31. Effect of throughput in shared links
Packet Loss
Another issue that severely affects the performance of
communication is the number of packets lost during
transmission. When a router receives a packet while
processing another packet, the received packet needs to be
stored in the input buffer waiting for its turn. A router,
however, has an input buffer with a limited size. A time may
come when the buffer is full and the next packet needs to be
dropped. The effect of packet loss on the Internet network
layer is that the packet needs to be resent, which in turn may
create overflow and cause more packet loss.

32. Congestion Control
Congestion control is a mechanism for improving
performance. In Chapter 23, we will discuss congestion at the
transport layer. Although congestion at the network layer is
not explicitly addressed in the Internet model, the study of
congestion at this layer may help us to better understand the
cause of congestion at the transport layer and find possible
remedies to be used at the network layer. Congestion at the
network layer is related to two issues, throughput and delay,
which we discussed in the previous section.
Packet delay and throughput as functions of load

33. Backpressure method for alleviating congestion
Choke packet