CPSC Home

- August 2018
CPSC 341 - Assignments: 10/22 - 12/7
Earl Rodd [email protected] cpsc.rodd.us

Monday 10/22

Due:

• Wireshark Take Home Exam.
• Study "buffer bloat" to be ready for a quiz on Wednesday 10/24. The quiz will be closed book, but cover only the main concepts. Resources to study the issue are discussed below:
• https://en.Wikipedia.org/wiki/CoDel is a discussion of a proposed solution to the problem and has a good summary of the issue and the current status of solution implementation and is sufficient for all but one question on the quiz. However, other resources can help understand the problem.
• http://queue.acm.org/detail.cfm?id=2071893 Buffer Bloat - Black Buffers in the Internet - this is a very technical article on the nature of the problem. The first part of the article is an interesting story about how a researcher discovered the problem in his home Internet. Be sure you note the 1986 event that lead to the design and implementation of the current TCP congestion controls we have learned.
  Figures 1 and 2 will be printed with the quiz. Be sure you understand them.
• http://queue.acm.org/detail.cfm?id=2076798 Buffer Bloat - What's Wrong With the Internet This is a discussion among several leading Internet designers. No quiz questions concern these comments, but you might find it interesting reading and helpful to understand the problem.
• http://queue.acm.org/detail.cfm?id=2209336 Controlling Queue Delay (CoDel) This is the original paper proposing a solution that has been implemented in a number of important places. The quiz will cover only the concept, not the details of simulations.

Class:

• Finish Link state vs. Distance Vector algorithms
• Introduce DHCP Wireshark Lab
• Explain Subnetting Exercise This can be done in hand - it's all numbers.
• ICANN and IP addresses (See notes).

Wednesday 10/24

Due:

• Wireshark DHCP lab.
• Subnetting Exercise You may print the form and fill it in by hand. You should make two copies - one to turn in, and one to write on when we go over the homework in class so you can use it as part of your study for the exam.
• Read section 5.3

Class:

• Review Wireshark Take Home Exam.
• Review subnetting exercise
• Routing

Friday 10/26

Due:
Class:

• Exam 2. Chapters 3 and 4. Study guide is here

Monday 10/29

Due:

• Wireshark traceroute lab.
• Chapter 5: R1, R2, Modified R5: Consider the "count-to-infinity" problem (top of page 390): Is it an example of: (briefly explain your answer).
  1. Good news travels quickly.
  2. Good news travels slowly.
  3. Bad news travels quickly.
  4. Bad news travels slowly.
  Modified R5b: Of the four choices above, which is also true of DV algorithms?, P1, P3(modified): Using LS logic, manually determine the shortest path from z-u and from x-t.
• Read section 5.4

Class:

• Closed book quiz on Buffer Bloat. Being closed book, this will cover only the main concepts. This counts as TWO daily assignments.
• Review exam
• Finish BGP

Wednesday 10/31

Due:

• Chapter 5: R7, R11, R13, R20, R22, R23
• Read chapter 5 sections 5.6 and 5.7. Note: We are not covering section 5.5 (SDN) at all.

Class:

• Finish chapter 5.
• Start chapter 6
• Discuss Wireshark ICMP lab.

Friday 11/2

Due:

• Chapter 5: P14a, b, c, d
• Wireshark ICMP lab.
• Read chapter 6.1.

Class:

• Continue chapter 6: Shared media.

Monday 11/5

Due:

• Chapter 6: R2, R4, R8, R9
• Read chapter 6.2 and 6.3.

Class:

• Handout the ARP lab work materials.
• Chapter 6: ARP, Switches and VLANs.
• Will not cover MPLS, section 6.5.
• We will explicitly cover sections 6.6 and 6.7. However, Reviewing them will be a good way to prepare for the next exam and put together all the pieces we have studied thus far.

Wednesday 11/7

Due:

• Answer these questions:
  1. In a protocol with collisions (e.g. shared Ethernet) what is the general effect on performance as utilization of link increases. Are the effects linear or non-linear?
  2. For DOCSIS, if many homes on the same CMTS are watching video streaming, what is the effect on performance as more people watch video? Is the effect linear or non-linear? Why?
  3. Again, for DOCSIS, many homes on the same CMTS are uploading home videos to websites. what is the effect on performance as more people upload video? Is the effect linear or non-linear? Why?
  4. Satellite Internet access uses protocols that have features of slotted Aloha and DOCSIS. The details tend to be proprietary to each company, but the basic principles are there. Satellite is inherently a shared medium like cable. What is different for satellite versus cable for the above two cases?
  5. What would happen if two hosts on the same Ethernet (which uses ARP) had the same MAC address. Try to construct a step-by-step scenario. Really good answers can get extra credit. (This can happen if the built in MAC address is intentionally over-ridden).
• Chapter 6: R10, R11, R12, R14, R15

Class:

• Chapter 6.
• Review network startup
• Start Security - chapter 8. My goal is to cover sections 8.1 - 8.4 except for the math details of RSA. We will hopefully have time to pick one or two of the various applications of the principles of security from 8.1-8.4 which are covered in later sections.

Friday 11/9

Due:

• What would happen if two hosts (in the same subnet) are mis-configured to have the same IP addess? Try to construct a step-by-step scenario. Really good answers can get extra credit.
• Chapter 6: P14, P15. For P14, draw a network diagram (can be by hand) with the various addresses. To save busy-work, use simplified MAC addresses of the form n:m (e.g. 2:1), P23MODIFIED: If one host in Elec. Eng is sending at full speed to another host in Elec. Eng, and the third host in Elec. Eng is downloading from the web server, what is the maximum speed of the download? Why? Also, under ideal conditions, what is the maximum aggregate rate that the aggregate of all 9 hosts can download data from the EXTERNAL Internet assuming the servers are idle?

Class:

• Security 8.2

Monday 11/12

Due:

• ARP Lab work. The trace is available here. The console is here.. Note: I will handout printouts in class so you don't have to print these.

Class:

• Review homework from last Friday.
• Security: 8.2-8.4
• Quiz on just the TERMS in chapters 5 and 6. This will count as part of an exam. We will have an exam later. TERMS means the questions are short and do not require comparisons or complex consideration of scenarios. Study Guide is here.

Wednesday 11/14

Due:

• Chapter 8: R1, R3, R4, R6
• Answer these questions:
  1. Your job is configure a server with a fixed IP address. What four data items must you know about your network to enter into the configuration? (If you have admin access to a Windows machine, you can look at the config page for networking).
  2. Data is encrypted using AES. What does a person need to know to decrypt the data?
  3. Data is encrypted using the public key found in a certificate. What does a person need to know to decrypt the data?
  4. Data is encrypted using the private key associated with a certificate. What does a person need to know to decrypt the data?
• Alice and Bob are sending messages to each other. They have a shared secret AES key. They are using a custom TCP application which is peer-peer between each other. Trudy is a "man-in-the-middle" on a link between routers on the path which are connected with Ethernet. She can modify data, but does not know the key. ("Trudy" might be law enforcement.) Answer these questions:
  1. If Trudy modifies some bits of the message, but not the CRC. What happens?
  2. Is there any way Trudy can modify the message so that the Ethernet CRC will still be correct? If she can, what happens?
  3. Can Trudy tell what IP address Alice and Bob are located at? Why or why not?
  4. What happens if Trudy changes the TTL in the IP header to 1? Can she do this?
  5. Extra challenge: What could Trudy change that would allow a message to get from Alice to Bob, but cause Alice's software to not know that Bob got the message? (The software assumes that if the TCP messages are ACKed, they got there).
     B. If instead of using TCP ACK to know if messages were delivered, the peer-peer app uses an encrypted application confirmation. Would the answer change?

Class:

• Review quiz
• Review ARP lab
• Review cryptology concepts: See these notes for a summary of concepts you should know.
• Chapter 8.3-8.4. See these notes for a quick overview of certificates.

Friday 11/16

Due:

• Chapter 8: R9, R10, R11, R12, R13
• Answer these questions:
  1. When you login to a bank (or shopping site) using https (TLS), where does your browser get the key used for the initial setup?
  2. If you go to the same bank later, having logged out the first time, will you use the same private/public key pair during setup?
     Will you use the same AES key as was used an hour earlier?
• Alice is sending data to Bob's web server encrypted using TLS. Bob's web server has a certificate from a recoginized CA. Trudy is a "man-in-the-middle" intercepting Ethernet frames between two routers on the path. She can not only see the data, but she can modify it. Answer these questions:
  1. What happens if after the TCP/TLS connection is setup, Trudy changes the source IP of data sent from Alice to Bob? Can she do this?
  2. Trudy herself connects to Bob's web server and obtains the certificate and thus public key. Can she use this to see any of the data?
  3. Assume that Alice does not authenticate (e.g. userid/password). Can Bob be confident that a given input came from Alice by noting her source IP address?
  4. What happens if Trudy intercepts the frame, takes the message apart and replaces it with different bits, and recomputes the checksums and Ethernet CRC?
  5. Change the scenario to have Alice "login" using userid/password. Trudy thinks she knows Alice's userid. Can she try fake passwords to see if she can find one that works?
  6. Change the scenario a little: Bob's web server uses a "self-signed" certificate created by Bob. There is standard software to do this. Only Bob knows the private key that goes with the certificate.
     A. Can Alice be sure she is communicating with Bob's web server?
     B. Trudy sets up a web server at her "man-in-the-middle" position. Can she impersonate Bob's web server?
     C. Assume Alice authenticates to Bob's server (userid/password). Could Trudy's web server impersonate Bob's by letting her login?

Class:

• Chapter 8 TLS

Monday 11/19

Due:

• DELETED R29, R30, R31. NO review questions due. Following question IS DUE!
• A vending machine communicates with an iPhone App. The user sets the app up online on a web site. The user pays for credits which are placed in the app. The user goes to the vending machine and makes a wireless Bluetooth connection to the machine and orders product (e.g. candy bar). The amount of purchase is subtracted from the amount of credit in the app. The vending machine advertised "military grade encryption" (i.e. AES). The phone does not need Internet access to buy product. Assuming the user can "reverse engineer" the app (i.e. by looking at the machine language code) to see how it works, can the user update his amount of "credit" without getting online to buy more? Why or why not? Assume no "bugs" in the app, just the inherent limits of the situation.

Class:

• Chapter 8: Review homework
• Security scenarios

Wednesday 11/21

Due:
Class:

• Thanksgiving Break

Friday 11/23

Due:
Class:

• Thanksgiving Break

Monday 11/26

Due:

• Integrated Networking Homework You can turn in this homework handwriting the answers on the form provided.
  Note: The second part of the homework requires you to check your IP address for an off-campus site! So do it over Thanksgiving break, NOT just before class on Monday!

Class:

• Finish discussions of security. Review homework.
• Quiz on terms - closed book EXCEPT you may have your copy of the study guide with you with your own notes on it. Count as 1/2 of an exam. It is comprehensive in the sense that the concepts from the various chapters are integrated, such as which layers process which headers and they layers communicate with each other. Study Guide is here.

Wednesday 11/28

Due:
Class:

• Exam 3. Covers chapters 5, 6, and 8. Study guide is here.

Friday 11/30

Due:

• From Adam Kelemann:
  I am pretty excited to cover the wireless chapter with you starting tomorrow. Please have the .1 and .2 chapter review questions (I think these are R1-R4 in your networking book's wireless chapter 7) completed as prework for our meeting tomorrow. I will collect them at the beginning of class. You might want to make a second copy to take notes on during class.
  See you at 1pm!

Class:

• Dr. Glasgow will return exam 3 to you. If you have questions or think I have made errors, email me. Please be specific about question number and your answer. A scan (or photo) of the page of the exam will be helpful. It may take a couple of days for me to respond, but I will.
• Wireless: Chapter 7.1 and 7.2

Monday 12/3

Due:
Class:

• Chapter 7.3 and 7.4 topics

Wednesday 12/5

Due:
Class:

• Chapter 7.5 and 7.6 topics

Friday 12/7

Due:
Class:

• Chapter 7.7 and 7.8 topics.
• Design scenario quiz

Wednesday 12/12 1-3PM

Final Exam Period - Guest Speaker - Attendance required to receive credit for course.