IS333 Spring 2015, Final Exam Take-home Question


Given the following network:




Machine M has just been connected to the network for the first time.  It gets its IP address from the DHCP server running on the NAT N.  Now the user who is logged into M runs a command called udpping, like this




This program creates a UDP packet with 50 bytes of random data in it, and sends it to the UDP echo port (7) on  That machine responds with a UDP packet back to the source.


Explain the various protocol messages that one would see going across the various links.  Explain what the various devices along this path do with those messages.  You do NOT have to tell me what the values are in all the fields in the messages, but you may want to or need to tell me what some values are in some fields – for example, to show that you understand what a NAT does.  You may also pick some MAC addresses for the interfaces to help you demonstrate what you know.


This was an interview question I used when I worked at a networking company.  Just as if you were in an interview with me, you want to impress me with your knowledge.  You are free to use any references you want (the book, the Internet, etc.), except other people.


Please type up your answer, print it out, and give the print out to me at the beginning of our exam time.