ISM6225-Assignment-1

ISM 6225: OSI Model Assignment #1 By Dr. Clinton Daniel and Dr. Manish Agrawal OSI Hands-on Fundamentals of Networking and Systems

1 Table of Contents OSI MODEL: INTRODUCTION .......................................................................................................................... 3 Lab 1 – Basic Linux Operating System commands ..................................................................................... 3 Exercise 1 – Working with directories .................................................................................................... 3 Lab 2 – Basic Linux Networking commands ............................................................................................... 7 Exercise 1 – Output the results of a network command to a text file ................................................... 7 Virtual Lab Exercise – Capture Linux Traceroute from Course Virtual Machine ....................................... 8 OSI MODEL: PHYSICAL LAYER ......................................................................................................................... 9 Lab 1 – Basic Linux Operating System commands ..................................................................................... 9 Exercise 1 – Coding data from ascii to binary ........................................................................................ 9 Exercise 2 – Coding data from binary to ascii ........................................................................................ 9 Lab 2 – Basic Linux Networking commands ............................................................................................. 10 Exercise 1 – Display network interface statistics ................................................................................. 10 Virtual Lab Exercise 1 – Code ASCII to Binary using Course Virtual Machine .......................................... 11 Virtual Lab Exercise 2 – Network Interface Statistics .............................................................................. 11 OSI MODEL: DATA-LINK LAYER ..................................................................................................................... 12 Lab 1 – Basic Linux Operating System commands ................................................................................... 12 Exercise 1 – Compute a Cyclic Redundancy Check (CRC) on a file ....................................................... 12 Exercise 2 – Hex and Binary representation of files ............................................................................. 13 Lab 2 – Basic Linux Networking commands ............................................................................................. 14 Exercise 1 – Understanding network interfaces .................................................................................. 14 Virtual Lab Exercise – Compute a Cyclic Redundancy Check (CRC) on a file ........................................... 15 OSI MODEL: NETWORK LAYER ...................................................................................................................... 16 Lab 1 – Basic Linux Operating System commands ................................................................................... 16 Exercise 1 – Convert bases to other bases using bc ................................... 16 Lab 2 – Basic Linux Networking commands ............................................................................................. 17 Exercise 1 – Capture IP packets using a host filter ............................................................................... 17 Virtual Lab Exercise – Convert bases to other bases ............................................................................... 20 OSI MODEL: TRANSPORT LAYER ................................................................................................................... 21 Lab 1 – Basic Linux Operating System commands ................................................................................... 21 Exercise 1 – Explore the ss utility ........................................................................................................ 21 Lab 2 – Basic Linux Networking commands ............................................................................................. 23 Exercise 1 – Using the client/server model to demonstrate the use of a socket ................................ 23

3 bdcuser@BDCVM:~$ pwd /home/bdcuser bdcuser@BDCVM:~$ ls bdcuser@BDCVM:~$ mkdir test bdcuser@BDCVM:~$ ls test OSI MODEL: INTRODUCTION Lab 1 – Basic Linux Operating System commands In this exercise you will be logging into the course virtual machine and executing some basic Linux Operating System commands. Learning how to navigate an operating system is an important practical skill for anyone whom desires to pursue a professional career in computer networking. Learning how to perform operating system tasks using the command line, as opposed to the graphical user interface (GUI) method, is important because most professional networking equipment is configured and managed using a command environment. Exercise 1 – Working with directories In this lab task you will learn to work with Linux directories. At the terminal command prompt, type the following command: The pwd command will output your current working directory. If you’ve typed this command following the login of your virtual machine it should output: The above output shows that your current directory is within a directory called bdcuser that is within the home directory. Notice that when working with Linux directories that they are delimited by forward slashes or /. This is noticeably different than Windows directories which are delimited by backward slashes or \. For instance, when viewing a directory in Windows the output may look like: C:\Users\Clinton. Now, type ls command to list the contents of the current working directory: Unless you have created a file or directory in /home/bdcuser, then your output from the ls command should be nothing. So, let’s add a directory first and then run the command again. To add a new directory, type the following command: The mkdir test command creates a directory called test in the current working directory. It is important to note that Linux directories are case sensitive. A directory called “test” is not the same as a directory called “ T est”. Now type the ls command again: Notice that now the output from the ls command shows the newly created directory called “test”.

4 bdcuser@BDCVM:~$ cd test bdcuser@BDCVM:~/test$ bdcuser@BDCVM:~$ cd ~ bdcuser@BDCVM:~$ touch hello-world hello-world bdcuser@BDCVM:~$ nano hello-world bdcuser@BDCVM:~$ man nano Also, it is common between terminal views to see the output of commands, directories, etc. in different colors. For instance, the output of ls in this terminal view displays the “test” directory in the color blue. Let’s navigate inside the newly created “test” directory from the current directory using the cd command: The output from the cd test command should show the terminal command prompt similar to the following: Notice that this time there is a /test after the ~ symbol. The ~ symbol is used in Linux to identify your home directory. So, in this case you are in the /test directory within your home directory. At any time, you can navigate back to your home directory by typing the following command: If you executed the cd ~ command, please navigate back to the “test” directory by typing cd test again. Now that you are back in the “test” directory you will want to create a new file called hello-world using the touch command that will reside in the “test” directory. To do this, type the following command: Notice that when we run the touch command above that there is no file extension. The command simply creates a file on the Linux Operating System that is empty. In other words, the file has no content. Now, run the ls command again and you should see the file listed as “hello - world”. Once you’ve created the empty file, you can edit the file using an editor. We will edit the “hello - world” file using the nano editor. For more information on the nano editor, visit the text editor homepage here: https://www.nano-editor.org/ . Run the following nano command: It is also helpful to know the man command. The man command loads the help manual for any command if one exists. For instance, to access the manual for nano you type the following command:

6 bdcuser@BDCVM:~$ cat hello-world Hello World Upon hitting CONTROL X on your keyboard, you will be prompted to Save your edited file: To save the edited file, you simply hit the Y key on your keyboard (as seen above with Y Yes ). Then, you may have to hit the Enter key on your keyboard to re-display the command prompt. You can now view the contents of the file you have created, edited, and saved using the following cat command: The output from the cat hello-world command should show the contents of your file: * Other useful commands for working with Linux directories can be found on the Debian Wiki here: https://wiki.debian.org/ShellCommands

7 bdcuser@BDCVM:~$ sudo mount -t vboxsf vmshare ~/capture bdcuser@BDCVM:~/capture$ bdcuser@BDCVM:~/capture$ traceroute www.google.com>data.txt bdcuser@BDCVM:~$ cat data.txt Lab 2 – Basic Linux Networking commands In this exercise you will be executing the traceroute network command and sending its output to a text file called data.txt. Exercise 1 – Output the results of a network command to a text file First, you will need to navigate to the shared directory setup from your home directory. Please be sure that your virtual machine is setup based on the instructions provided with the Lab Manual. The setup instructions include a section which explains how to setup a local shared directory so that you can move files from your course virtual machine to a directory on your local laptop or PC. If you have setup your local shared directory as instructed in the virtual machine setup instructions, execute the following command to mount the shared directory called capture: When prompted, be sure to put in the password for the bdcuser account as instructed in the course virtual machine setup. Once you mount the “capture” directory to your local laptop/PC, execute the cd ~/capture command. The output from the cd ~/capture command should navigate you to the “capture” shared directory. Your output should look like this: Once you are in this directory, execute the following command: NOTE: Please be patient while this command runs. The cursor on the screen will just blink for a while the command collects the network data. It may take a minute or so depending on the speed of your network connection. When the command completes, you will see the command prompt re-display. Once the command has completed, you can type in the ls command. You should see the data.txt file. To view the contents of the file in Linux, run the following command: Upon execution of the cat data.txt command, you should see all the output of the traceroute command. The traceroute command collects data on the route that a packet will take to reach a destination. In this example the destination is www.google.com . As you observe the output of the command, each number listed in each row represents a new hop in the route to the destination. Each hop includes an IP address that supports an interface to route the packet toward the next hop. Additionally, each hop shows how many milliseconds it took for the interface to respond to the request. You may now minimize the Linux virtual machine and navigate to your local laptop or PC shared directory to access the data.txt file on your host operating system (ex. Windows or Mac OS X).

9 bdcuser@BDCVM:~$ echo -n “h” | xxd -b 00000000: 01101000 bdcuser@BDCVM:~$ echo 01101000 01100101 01101100 01101100 01101111 | perl - lape ‘$_=pack“(B8)*”,@F’ OSI MODEL: PHYSICAL LAYER Lab 1 – Basic Linux Operating System commands In this exercise you will be logging into the course virtual machine and executing some basic Linux Operating System commands. Learning how to navigate an operating system is an important practical skill for anyone whom desires to pursue a professional career in computer networking. Learning how to perform operating system tasks using the command line, as opposed to the graphical user interface (GUI) method, is important because most professional networking equipment is configured and managed using a command environment. Exercise 1 – Coding data from ascii to binary In this lab task you will learn to code data using the Linux xxd command. If you read the xxd manual, it describes the xxd command as having the ability to create a “ hex dump of a given file or given input. It can also convert a hex dump back into its original binary form. ” To read more about the xxd command, type man xxp at the terminal command prompt. First, let’s start with a simple command to convert the letter “h” into binary. At the terminal command prompt, type the following command: The command in the example above converts the ascii character “h” to the binary 01101000. You can re - use the command above to convert other ascii characters to binary by just substituting the letter “h” with any other ascii character. From the above command, echo is the command to print a string to the standard output. The -n after echo is used so that there is no trailing newline. To learn more about the echo command, type man echo from the command prompt. Following the echo -n command is the “h”. This is the explicit ascii character that is being printed. Next is a pipe | character. The pipe character is used to delimit commands. The next command is the xxd -b . The -b commands xxd to switch the “h” ascii character to bits or binary digits. The -b option writes octets as eight digits. This is why you will see 8 zeros with a colon (:) followed by the 8-digit binary translation (or octet). The output of the above command should look like the following: Exercise 2 – Coding data from binary to ascii It is useful to understand that network professionals often use scripting languages to work with data. A common scripting language available within Linux distributions is Perl. To learn more about Perl, type man perl from the terminal command prompt. Below is an example of a command that uses Perl script to code binary data to ascii characters. Now, type the following command: The output from the above command (displayed again below) should be the ascii characters “h e l l o”. echo 01101000 01100101 01101100 01101100 01101111 | perl -lape ‘$_=pack“(B8)*”,@F’

10 bdcuser@BDCVM:~$ ifstat First, the command starts with the echo command. As described in Exercise 1 above, the echo command is simply used to print a string to the standard output. Here, the echo command is followed by a series of 5 octets in binary. Next, the command presents the delimited pipe | to allow for the next command. The next command includes a Perl script. Notice that there is a -lape after the perl command. Anytime you use the dash – after the perl command, this is called a command line argument. Therefore, -lape includes 4 separate command arguments executed in the order listed. For instance, the command argument -l would be executed before -a , and so forth. The command line argument for this Perl script, -lape , commands the script to basically read in the string generated from the echo command and loops through each character. Then it uses the pack function to convert the octet (groups of 8 characters) to an ascii character. Finally, the Perl script prints the output of the pack function to the screen. You can learn more about Perl’s pack function here: https://perldoc.perl.org/functions/pack.html Lab 2 – Basic Linux Networking commands In this exercise you will be executing the ifstat command to report interface statistics on your device. Exercise 1 – Display network interface statistics The Physical Layer of the OSI model sends data as signals over a physical medium. The ifstat utility is designed to report simple statistics from the interfaces connected to the physical medium. Execute the following command and wait about 5 seconds while it executes. Hit CNTRL C on your keyboard to stop the command: Your output should look something like this, but with more rows of data: enp0s3 KB/s in KB/s out 0.19 0.00 0.0 0.00 In the output from the ifstat command above, you can see the name of your interface first. In this case, the interface is labeled “ enp0s3 ”. Next, you will see two columns of data. One column lists the data moving in the interface at a rate in KB/s (Kilobytes per Second). The second column lists the data moving out of the interface at a rate in KB/s.

12 bdcuser@BDCVM:~$ cksum data.txt 2116921653 13 data.txt 1949538277 41 data.txt OSI MODEL: DATA-LINK LAYER Lab 1 – Basic Linux Operating System commands When files are transferred or data is streamed over a network from a source to a destination, it is common for network professionals to verify the integrity of the data or file. Verifying the integrity of a file can be accomplished by conducting a Cyclic Redundancy Check (CRC) on the data. CRC can be accomplished using the Linux cksum command. To learn more about the cksum command, type cksum --help at the terminal command prompt. Exercise 1 – Compute a Cyclic Redundancy Check (CRC) on a file Review Exercise 1 from Chapter 1 Lab 1. Navigate to a directory of your choice on the course virtual machine and create a text file called data.txt . Use nano to edit the file and add some data by typing “Hello World!”. Exit nano and save the file. Now, execute the following cksum command on the data.txt file: You should get output in the terminal similar the to the following after executing the above cksum command: In the above output, the cksum command is first displaying the checksum (CRC output), the second number is the number of bytes, and finally the name of the file is displayed. NOTE: Your output may be different from the output above. Based on the output above, the CRC is computed as 2116921653 with 13 bytes of data in the data.txt file. Now, use nano to edit the data.txt file. Add the following text to the file, “Making a change to the data”. Exit nano and save the changes to the data.txt file. Once you have done this, re-execute the cksum data.txt command. Your output should look similar to the following: ( NOTE: Your output may be different). Since the file has been edited, the CRC is computed by checksum with a different identity (1949538277). Additionally, you can see that the byte size of the data.txt file has increased from 13 bytes to 41 bytes. If a network professional was monitoring the integrity of a file being transferred from a source to a destination over a network connection, he or she would want to execute a checksum (CRC) on the file before the transmission and after the completion of the transfer. If the identity of the computed checksum is different when comparing before and after the transfer, then it is indicative that data may have been corrupted or altered in some way. Therefore, computing a CRC on a file or data is very important to network professionals when moving data over a network.

13 bdcuser@BDCVM:~$ xxd data.txt bdcuser@BDCVM:~$ xxd -b data.txt Exercise 2 – Hex and Binary representation of files The Linux xxd command (as described in its documentation) can be used to perform a “ hex dump of a given file or standard input ”. Navigate to the directory you created the data.txt file in Exercise 1 of this Lab 1. You will first convert the contents of the data.txt file to hex. To do this, execute the following command: The output of the above xxd command will look similar to the following ( NOTE: Your output may have different hex values): In the above output, you can see the text “Hello World! Making a change to the data” on the right includes the content in the data.txt file. To the left of this text, you can see the hex values of this content. Also notice that there is a period (.) after “Hello World!” and after “Making a change to the data”. In this case, the period(.) is indicative of a next line feed. So, if you were to view the content of the data.txt file, it would look like this: Hello World! Making a change to the data Next, we can use the xxd command to produce binary from the data.txt . To do this, execute the following command: The output of the above xxd command will look similar to the following ( NOTE: Your output may have different binary values): The above output is similar to the previous output. The only difference is that the -b argument of the xxd command produced the binary values of the content included in the data.txt file.

15 Virtual Lab Exercise – Compute a Cyclic Redundancy Check (CRC) on a file Review Exercise 1 in Lab 1 for the Data Link Layer in the course Lab Manual. Complete the following steps: 1. Create a text file called “ mymessage.txt ”. 2. Open the file using nano and edit the file with the following text, “Learning how to compute a Cyclic Redundancy Check on a file” 3. Now, exit nano and save the file. 4. Use the cksum command to compute a Cyclic Redundancy Check on the mymessage.txt file What output did you get from this command? Explain each part of the output. Next, complete the following steps: 1. Re-open the mymessage.txt file in nano and edit the file with by typing your First and Last name on the next row. 2. Exit nano and save the file. 3. Use the cksum command to compute a Cyclic Redundancy Check on the mymessage.txt file What output did you get from this command? What was the difference in the output of this command versus the first time you executed the command? Why do you think it is important for a network professional to know how to conduct a Cyclic Redundancy Check on a file?

16 bdcuser@BDCVM:~$ echo “obase=2;133” | bc 10000101 bdcuser@BDCVM:~$ echo “ibase=2;10000101” | bc 133 OSI MODEL: NETWORK LAYER Lab 1 – Basic Linux Operating System commands It is a common skill for network professionals to use tools in Linux which can perform various precision tasks on numbers. For instance, a common precision task would be to convert an integer base to binary base or binary base to an integer base. According to the documentation, bc is “a language that supports arbitrary precision numbers with interactive execution of statements ”. You can learn more about bc by typing man bc at the terminal command prompt. Exercise 1 – Convert bases to other bases using bc To convert the integer 133 to binary using bc , execute the following command: You should get output in the terminal similar the to the following after executing the above bc command: To convert the binary 10000101 to an integer using bc, execute the following command: You should get output in the terminal similar to the following after executing the above bc command:

18 bdcuser@BDCVM:~$ ping 8.8.8.8 bdcuser@BDCVM:~$ sudo tcpdump -i any -c5 -nn host dns.google Notice in the screen shot of PuTTY above that the Port is set to 22. This is the common port used for ssh . After clicking Open you will be prompted to enter your username and password. Use the same username (bdcuser) and password you typically use to login to your course virtual machine. STEP 4: Execute a tcpdump command Once you have logged into your remote session using either PuTTY or the Mac Terminal app, you will need to execute the ping command so that your virtual machine can capture requests and replies from IP packets that are related to a specific host. From the PuTTY or Mac Terminal app connection client, type the following command (8.8.8.8 is the IP address assigned to Google’s primary DNS (Domain Name System) server for Google DNS): Once you have typed in the above ping command in the PuTTY or Mac Terminal app connection client, you will see a continuous output similar to the following: Allow this continuous ping to continue without interruption. Minimize the PuTTY or Mac Terminal app and return to your course virtual machine (launched by VirtualBox). From the virtual machine terminal command prompt, type the following tcpdump command from any directory (add your bdcuser username and password when prompted to):

19 The output from this tcpdump command should produce output similar to the following: Once your tcpdump is complete, you will need to click ( NOTE: make sure it is clicked on ) back on to the PuTTY or Mac Terminal app connection client to stop the ping process. To stop the ping process, simply type CNTRL +C (Control and C at the same time) on your keyboard. In the above tcpdump output, you can see that it has captured 5 packets of data. The filter in the tcpdump command will capture any 5 packets ( -c5 ) from any port ( -nn ) that includes the host dns.google . Since we are pinging 8.8.8.8, tcpdump can detect the packet requests and replies from Google’s DNS server or host. Each packet captured includes the datagram timestamp, source IP address, destination IP address, protocol, information from the protocol, the id identifying the fragmented part of the datagram, the sequence number, and the packet length. For instance: 00:00:08.458155 IP 192.168.1.103 > 8.8.8.8: ICMP echo request, id 862, seq 39, length 64 Can be interpreted as: 00:00:08.458155 = the datagram timestamp IP = Internet Protocol 192.168.1.103 = Source IP address (local PC/Laptop) 8.8.8.8 = Destination IP address (Google’s DNS Server host) ICMP = Internet Control Message Protocol echo request = ICMP information id 862 = the id of the fragmented part of the datagram seq 39 = the sequence number length 64 = the length of the packet