COIT20261 Network Routing and Switching (pdf)

COIT20261 Network Routing and Switching (Term 1, 2018)
Assignment item —Written Assessment-2
Due date: 11:45pm AEST, Friday, Week 10 ASSESSMENT
Weighting: 25% 2
Objectives
This assessment task requires you to demonstrate your knowledge of routing concepts by
completing a number of exercise questions.
The questions are designed to help you to achieve the unit learning outcomes as listed in the
unit profile.
Instructions
You must do this assignment on your own – it is not a group assignment.
These questions will require more time and effort than the first assignment so plan ahead and
start as early as possible. Question #3 may require additional research and analysis to
complete.
Type all your answers in the ‘Template for Your Answers’ Section of this document and
upload only that template. You can do that by copying the Template section into a new Word
document for uploading. Answers that are not typed into the “Template for Your Answers”
section may not be marked, or may be returned to you for re-typing and re-submission – late
penalties will apply.
Where instructed, you must show the steps you took to arrive at your answers. Write
your answers in your own words to avoid potential plagiarism and copyright violations.
You must submit the Answer section as a Word file (.doc or .docx). Do not submit PDF’s
or any other type of file without express permission from the Unit Coordinator.
Plagiarism Procedures can be found in the CQUniversity Policies section of the Unit Profile.
Assessment Requirements and Marking Criteria
There are 3 main questions each with sub-questions and the requirements are stated for each
one. You must answer all questions and their sub-questions. Marks are indicated in the
Answer Template.
The questions will be marked on correctness, logic and clarity, and addressing all parts of the
question.
The Assignment Questions begin on the next page.
REMEMBER, USE THE ANSWER TEMPLATE FOR ALL YOUR ANSWERS

COIT20261 Network Routing and Switching (Term 1, 2018)
Assignment item —Written Assessment-2
Question 1 – Routing (10 marks)
Given the following network diagram, assume that all the networks shown are aware of each
other and have fully updated routing tables. Answer the questions that follow.
The questions (1 mark each except q.8):
1. From the point of view of router R4, what is the next-hop address for a packet
addressed to host 161.22.0.15/18?
2. From the point of view of router R1, which of its interfaces would it choose for a
packet being sent to network 161.22.0.0/18?
3. A host with an IP address of 200.11.60.36/24 has just sent a packet to a host with
address 150.32.0.240/18. How many hops is required between source and
destination?
4. A packet originating from network 220.10.40.0/24 arrives at router R1, however, R1
determines that the destination network is not in its routing table. What does R1 do
with the packet?
5. A packet arrives at router R2 with a destination address of 140.21.0.10/22. Which
interface port does R2 forward the packet out of?
6. A packet at router R3 has a destination address of 220.10.40.5/26. What next-hop
address would R3 use for this packet?
7. A packet is waiting at router R4 for forwarding. If the next-hop was a “direct
delivery”, which of these three networks is the destination network? 150.3.0.0/16, or
150.32.0.0/18, or 220.10.40.0/24?

COIT20261 Network Routing and Switching (Term 1, 2018)
Assignment item —Written Assessment-2
8. Complete the information in the routing table for router R2 as shown in the Answer
Template for networks 150.3.0.0/16, 150.32.0.0/18, and the Default network. Show
the masks in longest mask order using CIDR format (3 marks).
Question 2 – Fragmentation in IPv4 (5 marks)
An IP datagram 5,400 bytes long with no options arrives at a router, which determines that
the next destination has an MTU of 1,500 bytes. Use the Answer Template to complete the
following questions, showing your calculations and reasoning.
a) Assuming that the router decides to fragment the packet into 4 fragments, determine a
correct size for each fragment, and identify the starting byte and ending byte of each
fragment (2.5 marks).
b) Calculate the fragmentation offset for each fragment (1.5 marks).
c) State whether the total number of bytes from all 4 fragments leaving the router will be
greater than the initial datagram size that arrived, or less than the initial datagram size,
and the reason (1 mark).
Question 3 – Congestion controls in TCP (10 marks)
This question affords you the opportunity to extend your thinking about congestion controls
in TCP beyond the textbook to observe what a real-world technology company, Google, is
doing in this space.
First, read this Network World article that reports on Google’s approach to improving
congestion controls in TCP:
https://www.networkworld.com/article/3218084/lan-wan/how-google-is-speeding-up-the-
internet.html?
idg_eid=f32fc7aec843db7ef67d0a4f08e3322d&email_SHA1_lc=&cid=nww_nlt_networkworld_daily_
news_alert_2017-08-22&utm_source=Sailthru&utm_medium=email&utm_campaign=NWW
%20Daily%20AM%20Alert%202017-08-22&utm_term=networkworld_daily_news_alert
You should also read the following more technical paper about it: https://tools.ietf.org/id/draft-
cardwell-iccrg-bbr-congestion-control-00.html
After reading both articles, answer the following questions:
1. Write a brief summary of the congestion controls currently available in TCP as
covered in this Unit (1 mark)
2. Identify and explain two problems with current congestion controls in TCP that are
pointed out in the articles (2 marks)
3. Summarize in your own words the difference(s) between the current TCP congestion
controls and Google’s new BBR protocol (3 marks)

COIT20261 Network Routing and Switching (Term 1, 2018)
Assignment item —Written Assessment-2
4. The Network World article points out that it is difficult to get a new protocol accepted
as a global standard for TCP/IP. Why do you think this is the case? Give carefully
thought out reasons for your answer. (4 marks)
Important: for every direct quotation you use from these two sources or any other source, you
must immediately, after the quote, provide your own explanation of the quotation (for example,
explain why are you quoting it, how does it help answer the question, how does it support what you
are saying?) – marks will be deducted for failure to do so. In addition, correct referencing
conventions must be used throughout your work using the Harvard referencing convention. Your
answers will be marked on clarity, logic, relevance, use of own words and fully addressing all parts of
each question.
Remember that quotations alone will not be accepted as your explanation of the questions.
Quotations can support your explanations, but you must still provide the explanations yourself.
Best way forward is to keep direct quotations to a minimum, and use your own words.

COIT20261 Network Routing and Switching (Term 1, 2018)
Assignment item —Written Assessment-2
TEMPLATE FOR YOUR ANSWERS
Type your answers in this section in the spaces provided. Spaces
can expand as you type.
First Name:_________________________ Last Name:____________________________
Student ID: __________________________
Question Number Mark
allocated
Marks
earned
Question 1: (10 marks)
1.
2.
3.
4.
5.
6.
7.
8.
150.3.0.3/16
m0 that is 150.3.0.3/16
2 hops
It drops the packet
m0 150.0.0.4/16
150.3.0.3/16
150.3.0.0/16
q.8 Routing table of router R2:
Prefix Network
address
Next-hop address Interface
16 150.3.0.0 150.3.0.1 m0
18 150.32.0.0 150.3.0.1 m0
150.3.0.4/
16
150.3.0.0 150.3.0.1
150.3.0.2
150.3.0.3
m0
m0
m0
1-7 1
mark
each, q.8
3 marks
Question 2: (5 marks)
a) Datagram = 5400bytes MTU = 1500 bytes IP header = 20 bytes
1500-20 = 1480 bytes of data may be transmitted in each packet
1st packet = 20 bytes IP header and 1480 data. Size = 1480+20 = 1500
Starting byte =1 ending byte = 1480
2nd packet = 20 bytes IP header and 1480 data. Size = 1480+20 = 1500
Starting byte =1481 ending byte = 2960
3rd packet = 20 bytes IP header and 1480 data. Size = 1480+20 = 1500
Starting byte =2961 ending byte = 4440
4th packet = 20 bytes IP header and 940 data. Size = 940+20 = 960
Starting byte =4441 ending byte = 5460
2.5
b) 1480/8 = 185 1.5

COIT20261 Network Routing and Switching (Term 1, 2018)
Assignment item —Written Assessment-2
1st offset = 0
2nd offset = 185
3rd offset = 370
4th offset = 555
c) The IP header is always 20bytes and is the same in each packet therefore the
size of the next datagram is reduced automatically by 20 bytes than the
previous one. Example, the number of bytes in the first packet is 1500 and the
starting number of bytes in the second packet is 1481. This is because of the IP
header. Therefore the total number of bytes should be greater than the initial
datagram size that has arrived
1
Question 3: (10 marks)
1. The TCP is designed to slow down traffic when it senses that there is congestion
which is determined by monitoring the number of packets lost. This was not an
efficient way because a loss of packets means loss of data. “if TCP only slows
down traffic when it detects packet loss, then it’s too little too late.” (van
jacobson). This shows that this method was not efficient enough to protect the
loss of packets in the first place. Secondly there are congestion control
algorithms namely reno and CUBIC, these algorithms determine the speed at
which to send data when congestion has been detected. The similarity between
these two controls is that they use packet loss to determine whether a network
is congested or not
1
2. The first problem with the current control methods is that they rely on loss of
packets to determine whether the traffic is congested or not. This is not
efficient because a loss of packets does not necessarily mean the traffic is
congested. “if TCP only slows down traffic when it detects packet loss, then it’s
too little too late.” (van jacobson).
The second problem is the network controls slow down the speed at which the
packets are being sent. This makes the network to become slower
2
3. Googles new BBR control does not wait until packets are lost to know the
network is congested, it determines the best path the packets will take whether
it is congested or not while the current controls determine whether the
network is congested when a loss of data packet occurs
3
4. It is time consuming. Standardizing congestion controls is not an easy task
hence takes a lot of time before the controls work well
Increase in bandwidth. The ever-continuing increase in bandwidth has made it
difficult to find a standard congestion control method. This creates a problem in
creating a congestion method that will last for long
Security. The current congestion methods including BBR use the same security
considerations. For another congestion control method to be adopted the
weakness in the security of the current methods should also be addressed in
depth
4
Total marks awarded 25 (max)

COIT20261 Network Routing and Switching (Term 1, 2018)
Assignment item —Written Assessment-2
Less late penalties if applicable
Less plagiarism penalties if applicable
Total marks earned
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