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(comp361)[2006](f)final~PPSpider^_10212.pdf
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COMP 361 Computer Networks
Fall Semester 2006
Final Examination (Marking Scheme)
Date: Dec. 13, 2006 Time: 8:30 am C 11:30 am
Name:_____________________ Student ID: ________________Email:__________________
Instructions
1.
Please write your name, student ID and email address on this page.


2.
Please answer all questions within the space provided on the examination paper. You may use back of the pages for your rough work. Please be concise, and this is NOT an essay contest.


3.
This paper consists of 8 questions and 13 pages.


4.
You have total 180 minutes to complete exam, thus each 10 points question roughly requires 18 minutes, please manage your time wisely.


5.
Please read each question very carefully and answer the questions carefully and clearly to the point. Make sure your answers are neatly written, legible, and readable.


6.
Show all the steps used in deriving your answer, wherever appropriate.




Question
Points
Score

1
10


2
16


3
15


4
15


5
15


6
9


7
8


8
12


Total
100





1.
Answer the following true/false questions by circling either T or F [10 points]




a)
Poison-reverse is used to solve the count-to-infinity problem in OSPF protocol. T F


b)
Class-A networks contain 8-bit subnet addresses. F


c)
A host can have more than one IP addresses F


d)
RIP is a link-state protocol T F


e)
Token Ring achieves better utilization than the Ethernet under heavy load F


f)
Both Router and Switch are plug-and-play devices T F


g)
The maximum throughput of pure ALOHA is much larger than that of slotted ALOHA.



T F
h)
BGP is used for intra-AS routing. (an Intra-AS protocol is one that routes within Autonomous Systems) T F


i)
Fairness can be guaranteed in TCP by the mechanism AIMD. T F


j)
Ethernet uses CSMA/CD as its multiple access protocol. F







2.
Give quick answer to the following questions [16 points].


a)





The above figure shows a simple BGP scenario. A, B, C, X, Y, W are interconnected autonomous systems. W, X, Y are stub networks and A, B, C are backbone provider networks. Consider the path information that reaches stub networks W, X and Y. Based on the information available at X, what is its view of the network topology? Justify your answer. As an example, the topology view at Y is shown below. [4 points]


Ans:

[3]


(1 point for each error).
In the above solution, X can get advertisements of either WAB or WAC and get advertisement of YC. [1]





b)
One problem with NAT is that it interferes with P2P applications. Suppose Peer A discovers that Peer B has a file it wants. Peer B is behind a NAT whereas Peer A is not. Let 138.76.29.7 be the WAN-side