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Welcome to Lesson
4
"How to Smash TCP/IP"

If you are clear with our previous Lessons we may
start with Lesson 4
By the end of this session, you will have a solid
grasp of the
theories that will help you understand the “Describe
How a Network
Works” section in my full CCNA course.

You will
learn to…

• Identify the different protocols and services
for each TCP/IP
Layer

• Differentiate TCP from UDP

• Understand the concept of IP Address

What is TCP/IP?
TCP/IP
is by far the most commonly used protocol in the networking
world.
It is considered as one of the major catalysts for the rapid
growth
of the Internet.

For this reason, knowing the TCP/IP concepts
will be instrumental to
ensure your success in getting CCNA
Certified.

TCP/IP is a suite of specialised protocols that is
based on the US
government’s Department of Defence (DoD) Model.

It
is the protocol of choice for both LANs and WANs because of its low
operating
cost. It is also highly flexible.

It can run on any platforms or
combination of network operating systems
and media. TCP and IP are
two distinct network protocols.

However, TCP and IP are so
commonly used together that TCP/IP has become
a standard.

The
TCP/IP Suite
TCP/IP is basically a condensed version of the OSI
stack. There are only
four layers, shown in the preceding table
along with its OSI
counterparts:

Figure 4.0 TCP/IP versus OSI

1.Application Layer
This layer is also known as the
Process Layer. It corresponds to the
three upper layers of the OSI
Stack. It has a wide array of protocols
that define how each
computer’s applications will interact with others.

Now,
be sure to pay attention to the protocols under this layer and be

acquainted with their functions. You will definitely encounter them
again
during the CCNA exam.

a.Telnet
Telnet is short for
“telephone network.” This protocol allows
text-mode type terminal
emulations. It permits a user to connect to a
remote computer by
logging in to a Telnet client.

Telnet can also be used to
configure and manage routers and
switches.

Figure 4.1 –
This is a Telnet interface screen

b.File Transfer Protocol (FTP)
FTP allows us to
transfer files by providing access to directories. It
also lets us
manage files and directories.

FTP requires user authentication
before allowing FTP access.
However, you can get around this by
using the “anonymous” username.
This type of access only allows
limited access to the user.

FTP is not only a protocol, it
is also an application program. Some
well know FTP clients are
CuteFTP, WS_FTP and FileZilla.

TFTP (Trivial FTP) is a
simplified version of FTP. It is only capable
of sending and
receiving files.

It does not have the ability to authenticate
users. It also does not
have the capacity to browse through
different directories like what
FTP does.

c.Simple Mail
Transfer Protocol (SMTP)
SMTP is used to send emails. Its
counterpart is Post Office Protocol
or POP3, which receives
emails.

As part of your comprehensive study for CCNA exams, you
should also
be aware of other application protocols such as

Simple
Network Management Protocol (SNMP), Domain Name Service (DNS),
Hyper
Text Transfer Protocol (HTTP), and Dynamic Host Configuration
Protocol
(DHCP)

2.Transport Layer
This layer is also known as
Host-to-Host Layer. It is equivalent to
the Transport Layer of the
OSI Stack.

Now, focus on the two protocols residing in this
layer. Both will
surely be covered by the CCNA exam. Don’t worry,
we will get into the
bare essentials of each.

a.Transmission
Control Protocol (TCP)
TCP is a full-duplex, connection-oriented
protocol that ensures a
reliable and error-free transfer of data.
That being said, it is very
complicated and costly in terms of
network bandwidth usage.

TCP establishes a connection between
the sending and receiving
devices through a three-way handshake as
shown in the figure below.

Figure 4.2 – The TCP three-way
handshake

TCP is responsible for segmenting the data stream it
receives from the
Application Layer. It is also its job to bring
segments back to the
original data format on the destination
device.

Here is the TCP segment format showing the header
fields and data.

Figure 4.3 – The TCP Format for segmenting Data
Streams

Did you notice that there are so many header fields in a
TCP segment?
TCP creates a lot of overhead and eats up a huge
amount of bandwidth.

In exchange of this, TCP guarantees a
highly reliable delivery of
data.

b.User Datagram Protocol
(UDP)
UDP is a connectionless protocol that serves as a faster,
simplified
alternative to TCP. UDP does not employ sequencing and
error-
checking measures.

It addresses the issues
regarding TCP’s excessive overhead by
significantly reducing the
number of header fields.

Figure 4.4 – The UDP segment header

For your CCNA preparation, consider memorizing
the table below. It
summarizes the features of TCP and UDP.

Figure
4.41 – TCP versus UDP

TCP and UDP uses port numbers in order to
communicate with the upper
layers. Port numbers range from 0 to
1023. You should also know by
heart the commonly used ports.

It can make or break your bid for a successful CCNA certification.

Figure
4.42: Port Table - Memorise the Port Numbers

3.Internet Layer
It is in this layer where
data segments are converted into packets. IP
selects a suitable
packet size. Then it proceeds to fragment larger
packets into
datagrams.

IP’s importance lies in its ability to control the
routing of data
across the network. It also provides a single
network interface to the
upper layers.

As the equivalent
of Network Layer in the OSI Stack, a number of
TCP/IP protocols
operate in the layer that we will discuss right now.

a.Internet
Protocol (IP)
IP is essentially the Internet layer. All the other
protocols in this
layer merely exist to support it. It has the
ability to oversee all
the networks and devices by using what we
call IP Address.

Depending on the destination IP of the packet,
IP will use a routing
table to decide the best path to route the
data in the network.

Keep in mind that IP is an unreliable,
connectionless protocol as
opposed to TCP. It provides for logical
addressing on the Network
Layer.

When IP receives a
segment from the upper layer, it fragments the
segment into a
datagram similar to the figure shown below.

IP then reassembles
the datagrams back into segments on the
receiving end.

Figure
4.5 – The IP header

b.Address Resolution Protocol (ARP)
ARP maps the IP
addresses to physical or hardware (MAC) addresses.
You can view
the ARP cache of a Cisco router by using the Show arp
command as
follows:

Figure 4.6 – ARP Cache using Telnet on Cisco Router

c.Reverse ARP (RARP)
RARP resolves physical
or hardware (MAC) addresses to IP addresses.
This is very helpful
for devices that are not capable of storing their
IP settings.

There must be a RARP server on the network in order for this to work.

d.Internet
Control Message Protocol (ICMP)
This protocol is mainly used for
control and messaging services. It is
also the protocol relating
to TCP/IP troubleshooting tools such as
ping (Packet Internet
Groper) and traceroute.

We will be talking about much more
TCP/IP network troubleshooting
techniques in the coming lessons.

4.Network
Access Layer
This is the lowest layer in the TCP/IP suite. It
provides the same
services as the Physical and Data Link layers of
the OSI stack.

And, as the layer closest to the network media,
it is in charge of
encapsulating datagrams into a format that is
manageable by the
physical network.

Addressing in TCP/IP
The
Internet Protocol (IP) uses a 32-bit identification number called IP
Address. All network components use the IP address to identify
themselves
in the network.

To make it easier for us humans to read, an IP
address is written in a
format called dotted decimal notation.This
format consists of four
numbers called octets, each separated by a
period.

Each octet can have a number rangingfrom 0 to 255 (28).
192.168.10.1 and
10.0.50.253 are just two of around 4.3 billion IP
addresses that we can
use!

Each IP address is paired with a
32-bit Subnet Mask. It informs the rest
of the network about which
segment or network the particular device
belongs to.

Like the
IP address, the subnet mask is also written in a dotted decimal

notation. An IP address can be assigned to a device in two ways:

Static
- IP address is manually set to a device.

DHCP (Dynamic Host
Control Protocol) – Automatically assigns a unique IP
address to a
network device

The steps below will teach you how to assign a
static IP address to a
Windows computer.

1. Click the
“Start” button, and then “Settings.”
2.Choose “Control Panel.”
3.Select the “Network Connections” icon from the list.

4.Click on the “Local Area Connection” icon.

This will open the
“Local Area Connection Status” dialog box.

Figure 4.7 – Network
Connections window

5.Click the “Properties” button on the lower left side.

6.Highlight the “Internet Protocol (TCP/IP)” option and click the
“Properties”
button.

Figure 4.8 – Local Area Connection properties dialog box

Select “Use the following IP address” option and
type in the desired IP
address.

Figure 4.9 – Internet
Protocol (TCP/IP) properties

8.Click the “OK” button.

9.To verify your IP
address, simply type ipconfig –all from the command
prompt.

Figure
4.10 – Using Ipconfig to display IP address.

We shall be dealing with more topics about IP
addresses more in the
coming lessons.

We have reached the end
of today’s lesson. We hope that you have
increased your
appreciation on TCP/IP Suite and all the protocols
associated to
each of its four layers.

As we have reached the halfway mark of
our CCNA Training course, you
should now be more conversant with
all the CCNA exam objectives that we
have discussed the past four
days.

In the next lesson of CCNA training, we will discuss
another key CCNA
topic, Remote Network Connectivity. It will surely
be another
interesting learning experience.

Just Give One
Hour Per Day to CCNA Training System.

Until then, Happy
networking!