FIT3165/FIT4165 Tutorial #2 TCP/IP Layered Architecture Week 3 – Semester 1 – 2022
01/03/2022
Revision Status
Updated by Dr. , Mar 2022.
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©2022, Faculty of IT, Monash University
Instructions
1. Students will work individually to solve this week’s exercise.
2. Please answer all the review questions asked in Task 1 and then try Task 2 work using
Wireshark.
Task 1 – Review Questions
Assume we add a new protocol to the application layer. What changes do we need to make to other layers?
Solutions: No changes are needed. The new protocol needs to use the services provided by one of the transport-layer protocols.
In the client-server paradigm, explain why a server (process) should be running all the time; While a client can initiate its request process when it is needed.
Solution: A server should always be on because a client may need to access it at any time. A client is normally the initializer of the connection; it can be run when it is needed.
A new application is to be designed using the client-server paradigm. If only small messages need to be exchanged between the client and the server without the concern for messages being lost or corrupted, what transport-layer protocol do you recommend?
Solution: In this case, UDP is more appropriate because it does not have the overhead of TCP in connection establishment and teardown.
FTP uses two separate well-known port numbers for control and data connection. Does this mean that two separate TCP connections are created for exchanging control information and data?
Solution: The answer is yes. Two separate connections are needed for setup and teardown to use FTP. FTP uses two TCP connections for communication.
• Executing an FTP port connection through a client is a two-stage process requiring the use of two different ports. Once the user enters the name of the server and the login credentials in the authorization fields of the FTP client, the FTP connection is established and the FTP control port of the FTP server (the default tcp port for sending commands is 21) is opened.
• Then a second connection to the server is made by the client, followed by a response of the FTP server from the port for sending data (the default data sending tcp port is 20), when the real file transfer actually begins.
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Using the FTP protocol, Can the client retrieve one file from the server site and store one file on the server site?If so, how many control connections and how many data transfer connections are needed?
Solution: YES, i.e. upload and download a file from the same server is possible. The task can be done using only one control connection, but two data-transfer connections are needed, one for retrieving and one for storing. Although the data-transfer connection is a two-way connection, one is used for data transfer, the other for acknowledging.
A source socket address is a combination of an IP address and a port number. Explain what each section identifies.
Solution: The IP address identifies the source computer; the port number identifies the source process.
Explain how a client process finds the IP address and the port number to be inserted in a remote socket address.
Solution: The client should either know the IP address of the server being communicated with or should know the name of the server (URL) and use the DNS to map the name to the IP address. The client should also know the standard well-known (TCP/UDP) port number of the corresponding server process.
Alice has a video clip that Bob is interested in getting; Bob has another video clip that Alice is interested in getting. Bob creates a web page and runs an HTTP server. How can Alice get Bob’s clip? How can Bob get Alice’s clip?
Solution: If Bob posts his clip on his website, Alice can get it by running an HTTP client (a browser) using a GET message. Since Alice is not running an HTTP server, she needs to use the PUT command and post her clip on Bob’s web site.
The TCP/IP suite, unlike the OSI model, has no presentation layer. But an application-layer protocol can include some of the features defined in this layer if needed. Does HTTP have any presentation layer features?
Solution: HTTP provides some presentation features, using the request and response headers. For example, HTTP messages can define the format and the language of the messages exchanged, which is a kind of presentation.
1.10 The TCP/IP suite, unlike the OSI model, has no session layer. However, an application-layer protocol can include some of the features defined in this layer if needed. Does HTTP have any session-layer features?
Solution: When HTTP operates in persistent-connection mode, it is actually implementing a session that can last for a period of time. This is simulating the session layer defined in the OSI model.
©2022, Faculty of IT, Monash University
Task 2 – Application layer protocols
This work is to understand the application layer protocols and how multiplexing and demultiplexing work in the transport layer.
Open Tutorial2_Example1.pcapng, a pre-captured Wireshark file and find the answers to the following questions by inspecting frames from 25 to 33.
Select 2.1.3.
Identify and name the application layer protocol used and identify the type of the service?
Application layer protocol used is HTTP, Hypertext Transfer Protocol. It is used for accessing the World Wide Web.
Identify and name the transport layer protocol used?
TCP, Transmission Control Protocol.
frame number 27 and answer the following questions What is the IP address of the destination?
Destination IP: 51.128.224.11
What is the IP address of the source
Source IP: 51.128.215.10
What is the HTTP version?
What is the Destination Port number
Destination port: 80
What is the Source Port number
Source port: 44168
Select frame number 29 and answer the following questions 2.1.8. What is the IP address of the destination?
Destination IP: 51.128.251.10
©2022, Faculty of IT, Monash University
2.1.9. What is the IP address of the source
Source IP: 51.128.224.11
2.1.10. What is the Destination Port number
Destination port: 44168
2.1.11. What is the Source Port number
Source port: 80
2.2. Open Tutorial2_Example2.pcapng, a pre-captured Wireshark file and find the answers to the following questions by inspecting frames from 12 to 35.
2.2.1. Identify and name the application layer protocol used and identify the type of the service?
Application layer protocol used is SMTP, Simple Mail Transfer Protocol. It is used by email servers.
2.2.2. Identify and name the transport layer protocol used?
TCP, Transmission Control Protocol.
Select frame number 26 and answer the following questions 2.2.3. What is the IP address of the destination?
Destination IP: 10.1.1.72
2.2.4. What is the IP address of the source
Source IP: 10.1.1.31
2.2.5. What is the Destination Port number
Destination port: 25
2.2.6. What is the Source Port number
Source port: 48604
©2022, Faculty of IT, Monash University
Select frame number 27 and answer the following questions 2.2.7. What is the IP address of the destination?
Destination IP: 10.1.1.31
2.2.8. What is the IP address of the source?
Source IP: 10.1.1.72
2.2.9. What is the Destination Port number?
Destination port: 48604
2.2.10. What is the Source Port number?
Source port: 25
Open Tutorial2_Example3.pcapng, a pre-captured Wireshark file and find the answers to the following questions by inspecting frames from 12 to 14.
Select 2.3.3.
Identify and name the application layer protocol used and identify the type of the service?
Application layer protocol used is DNS, Domain Name System. It is used to map a domain name to its corresponding IP address.
Identify and name the transport layer protocol used?
UDP, User Datagram Protocol
frame number 13 and answer the following questions What is the IP address of the destination?
Destination IP: 51.128.224.10
What is the IP address of the source?
Source IP: 51.128.215.10
What is the Destination Port number?
Destination port: 53
What is the Source Port number?
©2022, Faculty of IT, Monash University
Source port: 44565
Select frame number 14 and answer the following questions
What is the IP address of the destination?
Destination IP: 51.128.215.10
What is the IP address of the source?
Source IP: 51.128.224.10
What is the Destination Port number?
Destination port: 44565
2.3.10. What is the Source Port number?
Source port: 53
©2022, Faculty of IT, Monash University
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