FTP and TFTP



FTP and TFTP

CISC 856-010: TCP/IP and Upper Layer Protocols

Part 1

Read Chapters 20, 21 in TCP/IP Protocol Suite by Forouzan

Do problems ( Chapter 20: 1-14, Chapter 21: 1-16

Part 2

(A)

The acad machines do not run ftp daemons/servers – so students will not be able to ftp to the machines usually used in the assignments for this course. Therefore you will have to conduct these experiments by “ftping” to ren.eecis.udel.edu or strauss.udel.edu. You can ftp from the acad machines, but ftping to them doesn’t work.

You need a data-collection machine and a machine to act as a client. Create a small size file on the client and name it client.txt. Create four small files on the machine, which is running the ftp server (ren.eecis or strauss.udel.edu). Name them server1.txt, server2.txt…etc.

NOTE: You will need to keep track of two different ports (20 and 21), because ftp has two connections (control and data). Don’t just do tcpdump on the “ftp” port, as this, by default, monitors the control port (port 21) alone: “tcpdump port 21 or port 20” should work, or you can have two different tcpdump outputs.

1. Start tcpdump on the data-collection machine to monitor FTP traffic between the client and the FTP server.

2. From the client machine, ftp to the server using the command

ftp –d servername

[the –d flag turns on client debugging]

3. Upload the file client.txt to the server by using the command

put client.txt

4. Download the file server1.txt from the server by using the command

get server1.txt

5. Then download all the server*.txt files from the server by typing in

mget server*.txt

Pay attention to what happens when the mget command is used. You’ll notice it doesn’t act like a “normal” command. What you will undoubtedly notice is that there are several data connections for mget. You should note that mget will cause the server to first send a list of all the files that you specify (all .txt files beginning with “server”) to the client, and then the client will ask you, the user, one at a time, if you want a file. Each of those “yes” choices will cause a new data connection to be established, transferring a single file (and then closing the data connection, and repeating for each subsequent “yes”).

6. Exit ftp and then close tcpdump.

Turn in an annotated transcript of your tcpdump output and client output:

a. Indicate where the tcpdump control connection is made and broken.

b. Annotate your username and password being sent over the control connection

c. Indicate each data connection in the tcpdump output using different colors, and indicate what “data” is being transferred in each case; you need to be able to tell me what is going on in each data connection.

d. How many data connections can be seen in the tcpdump output?

e. If there was more than one data connection, do you see a change in the port numbers from one connection to another connection on either side? If you do notice a change, explain why the port numbers changed and if you have not noticed a change on either side for a particular connection, please explain why.

f. Who is initiating the data connections? Is it the server or the client machine? The FTP states that the server makes the data connection. If you witness the client initiating the data connection, give an explanation as to why this is happening.

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