Packet Tracer Simulation - TCP and UDP
Communications
Topology
Objectives
Part 1: Generate Network Traffic in
Simulation Mode
Part 2: Examine the Functionality of
the TCP and UDP Protocols
Background
This simulation activity is intended to
provide a foundation for understanding the TCP and UDP in detail. Simulation
mode provides the ability to view the functionality of the different protocols.
As data moves through the network, it is
broken down into smaller pieces and identified in some fashion so that the
pieces can be put back together. Each of these pieces is assigned a specific
name (protocol data unit [PDU]) and associated with a specific layer. Packet
Tracer Simulation mode enables the user to view each of the protocols and the
associated PDU. The steps outlined below lead the user through the process of
requesting services using various applications available on a client PC.
This activity provides an opportunity to
explore the functionality of the TCP and UDP protocols, multiplexing and the
function of port numbers in determining which local application requested the
data or is sending the data.
Part 1: Generate Network Traffic in Simulation Mode
Step 1:
Generate traffic to populate Address
Resolution Protocol (ARP) tables.
Perform the following tasks task to
reduce the amount of network traffic viewed in the simulation.
a.
Click MultiServer and click the Desktop
tab > Command Prompt.
b.
Enter the ping 192.168.1.255 command. This will take a few seconds as every
device on the network responds to MultiServer.
c.
Close the MultiServer window.
Step 2:
Generate web (HTTP) traffic.
a.
Switch to Simulation mode.
b.
Click HTTP Client and click the Desktop
tab > Web Browser.
c.
In the URL field, enter 192.168.1.254 and click Go. Envelopes (PDUs) will appear in the
simulation window.
d.
Minimize, but do not close, the
HTTP Client configuration window.
Step 3:
Generate FTP traffic.
a.
Click FTP Client and click the Desktop
tab > Command Prompt.
b.
Enter the ftp 192.168.1.254 command. PDUs will appear in the simulation
window.
c.
Minimize, but do not close, the
FTP Client configuration window.
Step 4:
Generate DNS traffic.
a.
Click DNS Client and click the Desktop
tab > Command Prompt.
b.
Enter the nslookup multiserver.pt.ptu command. A PDU will appear in the
simulation window.
c.
Minimize, but do not close, the
DNS Client configuration window.
Step 5:
Generate Email traffic.
a.
Click E-Mail Client and click the Desktop
tab > E Mail tool.
b.
Click Compose and enter the following information:
1)
To: user@multiserver.pt.ptu
2)
Subject: Personalize the subject line
3)
E-Mail Body: Personalize the Email
c.
Click Send.
d.
Minimize, but do not close, the
E-Mail Client configuration window.
Step 6:
Verify that the traffic is generated
and ready for simulation.
Every client computer should have PDUs listed
in the Simulation Panel.
Part 2: Examine Functionality of the TCP and UDP Protocols
Step 1:
Examine multiplexing as all of
the traffic crosses the network.
You will now use the Capture/Forward button and the Back
button in the Simulation Panel.
a.
Click Capture/Forward once. All of the PDUs are transferred to the
switch.
b.
Click Capture/Forward again. Some of the PDUs disappear. What do you
think happened to them?
_____They are stored on the switch_______________________________________________________________________________
c.
Click Capture/Forward six times. All clients should have received a
reply. Note that only one PDU can cross a wire in each direction at any given
time. What is this called?
_________Multiplexing__________________________________________________________________________
d.
A variety of PDUs appears in
the event list in the upper right pane of the simulation window. Why are they
so many different colors?
__They represent different protocols__________________________________________________________________________________
e.
Click Back eight times. This should reset the simulation.
Note: Do not click Reset
Simulation any time during this activity; if you do, you will need to
repeat the steps in Part 1.
Step 2:
Examine HTTP traffic as the clients
communicate with the server.
a.
Filter the traffic that is
currently displayed to display only HTTP
and TCP PDUs filter the traffic that
is currently displayed:
1)
Click Edit Filters and toggle the Show
All/None check box.
2)
Select HTTP and TCP. Click
anywhere outside of the Edit Filters box to hide it. The Visible Events should
now display only HTTP and TCP PDUs.
b.
Click Capture/Forward. Hold your mouse above each PDU until you find one
that originates from HTTP Client. Click
the PDU envelope to open it.
c.
Click the Inbound PDU Details tab and scroll down to the last section. What
is the section labeled?
______________TCP______________________________________________________________________
Are these communications considered to be
reliable?
________________Yes____________________________________________________________________
d.
Record the SRC PORT, DEST PORT, SEQUENCE NUM, and ACK NUM values. What is written in the field to the left of the WINDOW field?
___1025, 80, 0, 0 SYN _________________________________________________________________________________
e.
Close the PDU and click Capture/Forward until a PDU returns to
the HTTP Client with a checkmark.
f.
Click the PDU envelope and
select Inbound PDU Details. How are
the port and sequence numbers different than before?
______80, 1025, 0, 1 SYN-ACK. The syn
state change to SYN-ACK.______________________________________________________________________________
____________________________________________________________________________________
g.
There is a second PDU of a different color, which HTTP Client has prepared to send to MultiServer. This is the beginning of
the HTTP communication. Click this second PDU envelope and select Outbound PDU Details.
h.
What information is now listed
in the TCP section? How are the port and sequence numbers different from the
previous two PDUs?
_____1025, 80, 1, 1 PSH-ACK status change
SYN-ACK A PSH-ACK_______________________________________________________________________________
____________________________________________________________________________________
i.
Click Back until the simulation is reset.
Step 3:
Examine FTP traffic as the clients
communicate with the server.
a.
In the Simulation Panel, change
Edit Filters to display only FTP and TCP.
b.
Click Capture/Forward. Hold your cursor above each PDU until you find one
that originates from FTP Client.
Click that PDU envelope to open it.
c.
Click the Inbound PDU Details tab and scroll down to the last section. What
is the section labeled?
_________TCP___________________________________________________________________________
Are these communications considered to be
reliable?
________________Yes____________________________________________________________________
d.
Record the SRC PORT, DEST PORT, SEQUENCE NUM, and ACK NUM values. What is written in the field to the left of the WINDOW field?
_____1025, 21 , 0 , 0 SYN _______________________________________________________________________________
e.
Close the PDU and click Capture/Forward until a PDU returns to
the FTP Client with a checkmark.
f.
Click the PDU envelope and
select Inbound PDU Details. How are
the port and sequence numbers different than before?
____21, 1025, 0, 1 SYN-ACK ________________________________________________________________________________
____________________________________________________________________________________
g.
Click the Outbound PDU Details
tab. How are the port and sequence numbers different from the previous two
results?
______1025, 21 , 1 1 ACK ______________________________________________________________________________
____________________________________________________________________________________
h.
Close the PDU and click Capture/Forward until a second PDU
returns to the FTP Client. The PDU is
a different color.
i.
Open the PDU and select Inbound PDU Details. Scroll down past
the TCP section. What is the message from the server?
_____Welcome to PT FTP Server_______________________________________________________________________________
j.
Click Back until the simulation is reset.
Step 4:
Examine DNS traffic as the
clients communicate with the server.
a.
In the Simulation Panel, change
Edit Filters to display only DNS and UDP.
b.
Click the PDU envelope to open
it.
c.
Click the Inbound PDU Details tab and scroll down to the last section. What
is the section labeled?
_________UDP___________________________________________________________________________
Are these communications considered to be
reliable? ________No________________________
d.
Record the SRC PORT and DEST PORT values.
Why is there no sequence and acknowledgement number?
____1025, 53 Because UDP does not need to
establish a trusted connection________________________________________________________________________________
e.
Close the PDU and click Capture/Forward
until a PDU returns to the DNS
Client with a checkmark.
f.
Click the PDU envelope and
select Inbound PDU Details. How are
the port and sequence numbers different than before?
______53, 1025 ______________________________________________________________________________
g.
What is the last section of the
PDU called?
______DNS______________________________________________________________________________
h.
Click Back until the simulation is reset.
Step 5:
Examine email traffic as the clients
communicate with the server.
a.
In the Simulation Panel, change
Edit Filters to display only POP3, SMTP and TCP.
b.
Click Capture/Forward. Hold your cursor above each PDU until you find one
that originates from E-mail Client. Click
that PDU envelope to open it.
c.
Click the Inbound PDU Details tab and scroll down to the last section. What
transport layer protocol does email traffic use?
_____TCP_______________________________________________________________________________
Are these communications considered to be
reliable?
____________Yes________________________________________________________________________
d.
Record the SRC PORT, DEST PORT, SEQUENCE NUM, and ACK NUM values. What is written in the field to the left of the WINDOW field?
__1025, 25 , 0, 0.SYN. __________________________________________________________________________________
e.
Close the PDU and click Capture/Forward
until a PDU returns to the E-Mail
Client with a checkmark.
f.
Click the PDU envelope and
select Inbound PDU Details. How are
the port and sequence numbers different than before?
___25, 1025, 0 1.SYN+ACK. _________________________________________________________________________________
____________________________________________________________________________________
g.
Click the Outbound PDU Details
tab. How are the port and sequence numbers different from the previous two
results?
___1025, 25 , 1, 1.ACK. _________________________________________________________________________________
____________________________________________________________________________________
h.
There is a second PDU of a different color that HTTP Client has prepared to send to MultiServer. This is the beginning of
the email communication. Click this second PDU envelope and select Outbound PDU Details.
i.
How are the port and sequence
numbers different from the previous two PDUs?
__1025, 25, 1, 1. PSH+ACK__________________________________________________________________________________
____________________________________________________________________________________
j.
What email protocol is associated
with TCP port 25? What protocol is associated with TCP port 110?
___SMTP, POP3_________________________________________________________________________________
k.
Click Back until the simulation is reset.
Step 6:
Examine the use of port numbers
from the server.
a.
To see TCP active sessions, perform
the following steps in quick succession:
1)
Switch back to Realtime mode.
2)
Click MultiServer and click the Desktop
tab > Command Prompt.
b.
Enter the netstat command. What protocols are listed in the left column? TCP______________________
What port numbers are being used by the server?
____25,80________________________________________________________________________________
c.
What states are the sessions
in?
_____Closed, Established, Last_Ack _______________________________________________________________________________
d.
Repeat the netstat command several times until you see only one session still
ESTABLISHED. For which service is this connection still open? FTP______________________________________________________
Why doesn’t this session close like the
other three? (Hint: Check the minimized clients)
___________The server is waiting for the password_________________________________________________________________________
Suggested Scoring Rubric
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Activity Section
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Question Location
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Possible Points
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Earned Points
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Part 2: Examine
Functionality of the TCP and UDP Protocols
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Step
1
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15
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Step
2
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15
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Step
3
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15
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|
|
|
Step
4
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15
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|
|
|
Step
5
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15
|
|
|
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Step
6
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25
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|
|
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Total Score
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100
|
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