3.2.4.6 Packet Tracer - Investigating The TCP-IP and OSI Models in Action KIM
3.2.4.6 Packet Tracer - Investigating The TCP-IP and OSI Models in Action KIM
3.2.4.6 Packet Tracer - Investigating The TCP-IP and OSI Models in Action KIM
Topology
Objectives
Part 1: Examine HTTP Web Traffic
Part 2: Display Elements of the TCP/IP Protocol Suite
Background
This simulation activity is intended to provide a foundation for understanding the TCP/IP protocol suite and
the relationship to the OSI model. Simulation mode allows you to view the data contents being sent across
the network at each layer.
As data moves through the network, it is broken down into smaller pieces and identified so that the pieces can
be put back together when they arrive at the destination. Each piece is assigned a specific name (protocol
data unit [PDU]) and associated with a specific layer of the TCP/IP and OSI models. Packet Tracer simulation
mode enables you to view each of the layers and the associated PDU. The following steps lead the user
through the process of requesting a web page from a web server by using the web browser application
available on a client PC.
Even though much of the information displayed will be discussed in more detail later, this is an opportunity to
explore the functionality of Packet Tracer and be able to visualize the encapsulation process.
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Packet Tracer - Investigating the TCP/IP and OSI Models in Action
What is the common information listed under the TCP section of PDU Details, as compared to the
information listed under the OSI Model tab, and with which layer is it associated?
SRC PORT and DEST PORT at Layer 4
What is the Host listed under the HTTP section of the PDU Details? What layer would this information be
associated with under the OSI Model tab?
www.osi.local, Layer 7
k. Click the next colored square box under the Event List > Info column. Only Layer 1 is active (not grayed
out). The device is moving the frame from the buffer and placing it on to the network.
l. Advance to the next HTTP Info box within the Event List and click the colored square box. This window
contains both In Layers and Out Layers. Notice the direction of the arrow directly under the In Layers
column; it is pointing upward, indicating the direction the information is travelling. Scroll through these
layers making note of the items previously viewed. At the top of the column the arrow points to the right.
This denotes that the server is now sending the information back to the client.
Comparing the information displayed in the In Layers column with that of the Out Layers column, what
are the major differences?
The Src and Dst Ports, Src and Dst IPs and MAC addresses have been swapped.
m. Click the Outbound PDU Details tab. Scroll down to the HTTP section.
What is the first line in the HTTP message that displays?
HTTP/1.1 200 OK – this means that the request was successful and the page delivered from the
server.
n. Click the last colored square box under the Info column. How many tabs are displayed with this event and
why?
Inbound PDU Details because this is the receiving device.
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Packet Tracer - Investigating the TCP/IP and OSI Models in Action
is occurring is listed directly below the In Layers and Out Layers (“1. The DNS client sends a DNS query
to the DNS server.”). This is very useful information to help understand what is occurring during the
communication process.
d. Click the Outbound PDU Details tab. What information is listed in the NAME: in the DNS QUERY
section?
www.osi.local
e. Click the last DNS Info colored square box in the event list. Which device is displayed?
The Web Client
What is the value listed next to ADDRESS: in the DNS ANSWER section of the Inbound PDU Details?
192.168.1.254 – the address of the Web Server
f. Find the first HTTP event in the list and click the colored square box of the TCP event immediately
following this event. Highlight Layer 4 in the OSI Model tab. In the numbered list directly below the In
Layers and Out Layers, what is the information displayed under items 4 and 5?
4. The TCP connection is successful. 5. The device sets the connection state to
ESTABLISHED.
TCP manages the connecting and disconnecting of the communications channel along with other
responsibilities. This particular event shows that the communication channel has been ESTABLISHED.
g. Click the last TCP event. Highlight Layer 4 in the OSI Model tab. Examine the steps listed directly below
In Layers and Out Layers. What is the purpose of this event, based on the information provided in the
last item in the list (should be item 4)? CLOSING the connection.
Challenge
This simulation provided an example of a web session between a client and a server on a local area network
(LAN). The client makes requests to specific services running on the server. The server must be set up to
listen on specific ports for a client request. (Hint: Look at Layer 4 in the OSI Model tab for port information.)
Based on the information that was inspected during the Packet Tracer capture, what port number is the
Web Server listening on for the web request?
The first HTTP PDU being requested by the Web Client shows port 80 under the layer 4 DST
port.
What port is the Web Server listening on for a DNS request?
The first DNS PDU being requested by the Web Client shows a layer 4 destination of port 53.
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