Homework 14

Details

Do the following exercises from pages 195-196 of your textbook (183-184 in full book) and the ones below.

Problem	Points
1 below	6
2 below	6
3 below	12
43	4
45	6

1. Hope does not allow access to KnowHope from machines that are off campus without first entering a username and password.
   1. Which protocol layer would implement this type of restriction? Explain.
   2. How can Hope's web server determine whether or not a machine requesting access to KnowHope is on campus. Give your answer in terms of IP address, subnet mask, network base address, and an appropriate bit operation.
2. TCP, an implementation of the transport layer, breaks up messages into packets for transmission.
   1. Give two reasons why breaking messages up into packets is a good idea.
   2. TCP allows variable size packets; the size of the packet is stored in a fixed location in the packet. On a computer using a high-speed, highly reliable transmission medium such as a fiber optic cable, would it be better for TCP to use relatively small or relatively large packet sizes to increase the efficiency of data transfer? Explain your answer.
3. Being the unsavory sort of person you are, you decide to snoop on the network. You see the following packet:
   

   12:ab:22:83:f8:40|aa:02:ef:23:00:12|198.110.97.7|34.45.125.17|1175|25|2 of 4|nt to do somet
   

   Let S be the original source of the packet, D be the final destination, M1 be the intermediate node that this message just came from, and M2 be the intermediate node that this message is just being sent to. (Note: Keep in mind that it is possible that these are not 4 different machines.) Answer the following questions based on the information in the packet. Some of these questions cannot be answered given the information in the packet. In this case answer cannot be determined for certain.
   1. What is the IP address of S?
   2. What is the IP address of D?
   3. What is the IP address of M1?
   4. What is the IP address of M2?
   5. What is the Ethernet address of S?
   6. What is the Ethernet address of D?
   7. What is the Ethernet address of M1?
   8. What is the Ethernet address of M2?
   9. What is the port number of the application on S that sent the message?
   10. What is the port number of the application on D that the message is being sent to?
   11. What kind of application sent the message?
   12. What kind of application is the message destined for?

   Note: it is important to keep in mind that an actual packet will not look like the one above. It will just be raw data that needs to be interpreted to look like the packet above. An actual packet represented in hexadecimal might look like:

           12ab2283f840aa02ef230012e678fc9a128832e6ca89e38eecfdac23549acd0f0ae345ccff52e
   	

   To simplify things for you (so you don't have to do a whole lot of converting), I have simply interpreted the packet for you already. This comment has no bearing on this problem, but I thought it was important enough to point out.