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Assignment #3: Analysis of IP Protocol Solution
6 1 Goal
The purpose of this assignment is to learn about the IP protocol. You are required to write a
8 python program to analyze a trace of IP datagrams.
9 2 Introduction
In this assignment, we will investigate the IP protocol, focusing on the IP datagram. Well do so
by analyzing a trace of IP datagrams sent and received by an execution of the traceroute program.
We will investigate the various elds in the IP datagram, and study IP fragmentation in detail.
A background of the traceroute program is summarized as follows. The traceroute program
operates by rst sending one or more datagrams with the time-to-live (TTL) eld in the IP header
set to 1; it then sends a series of one or more datagrams towards the same destination with a TTL
value of 2; it then sends a series of datagrams towards the same destination with a TTL value of 3;
and so on. Recall that a router must decrement the TTL in each received datagram by 1 (actually,
RFC 791 says that the router must decrement the TTL by at least one). If the TTL reaches 0, the
router returns an ICMP message (type 11 TTL-exceeded) to the sending host. As a result of this
behavior, a datagram with a TTL of 1 (sent by the host executing traceroute) will cause the router
one hop away from the sender to send an ICMP TTL-exceeded message back to the sender; the
datagram sent with a TTL of 2 will cause the router two hops away to send an ICMP message back
to the sender; the datagram sent with a TTL of 3 will cause the router three hops away to send an
ICMP message back to the sender; and so on. In this manner, the host executing traceroute can
learn the identities of the routers between itself and a chosen destination by looking at the source
IP addresses in the datagrams containing the ICMP TTL-exceeded messages. You will be provided
with a trace le created by traceroute.
Of course, you can create a trace le by yourself. Note that when you create the trace le,
you need to use di erent datagram sizes (e.g., 2500 bytes) so that the captured trace le includes
information on fragmentation.
3 Requirements
There are two requirements for this assignment:
1
60 The IP address of the source node: 192.168.1.12
61 The IP address of ultimate destination node: 10.216.216.2
62 The IP addresses of the intermediate destination nodes:
63
router 1: 24.218.01.102,
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router 2: 24.221.10.103,
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router 3: 10.215.118.1.
66
67 The values in the protocol field of IP headers:
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1: ICMP
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17: UDP
70
71
72 The number of fragments created from the original datagram is: 3
2
59
The output format is as follows: (Note that the values do not correspond to any trace le).
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56
57
58
Calculate the average and standard deviation of round trip time(s) between the source node and the intermediate destination node (s) and the average round trip time between the source node and the ultimate destination node. The average and standard deviation are calculated over all fragments sent/received between the source nodes and the (intermediate/ ultimate) destination node.
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52
53
How many fragments were created from the original datagram? Note that 0 means no frag-mentation. Print out the o set (in terms of bytes) of the last fragment of the fragmented IP datagram. Note that if the datagram is not fragmented, the o set is 0.
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50
Check the IP header of all datagrams in the trace le, and list the set of values in the protocol eld of the IP headers. Note that only di erent values should be listed in a set.
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List the IP address of the source node, the IP address of ultimate destination node, the IP address(es) of the intermediate destination node(s). If multiple intermediate destination nodes exist, they should be ordered by their hop count to the source node in the increasing order.
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Your program needs to output the following information:
33 3.1
Requirement 1 (R1)
34 You are required to write a python program to analyze the trace of IP datagrams created by 35 traceroute. To make terminologies consistent, in this assignment we call the source node as the 36 computer that executes traceroute. The ultimate destination node refers to the host that is the 37 ultimate destination de ned when running traceroute. For example, the ultimate destination node 38 is \mit.edu" when you run
39 %traceroute mit.edu 2000
40 In addition, an intermediate destination node refers to the router that is not the ultimate destination 41 node but sends back a ICMP message to the source node.
42
As another example, you can set \don't fragment"' bit and set the number of probes per \ttl"
43 to 5 queries using the following command:
44 %traceroute -F -q 5 mit.edu 200
95 4
The offset of the last fragment is: 3680
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The avg RRT between 192.168.1.12 and 24.218.01.102 is: 50 ms, the s.d. is: 5 ms
The avg RRT between 192.168.1.12 and 24.221.10.103 is: 100 ms, the s.d. is: 6 ms
The avg RRT between 192.168.1.12 and 10.215.118.1 is: 150 ms, the s.d. is: 5 ms
The avg RRT between 192.168.1.12 and 10.216.216.2 is: 200 ms, the s.d. is: 15 ms
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80 3.2 Requirement 2 (R2)
Note: You can nish this part either with a python program or by manually col-
lecting/analyzing data. In other words, coding is optional for the tasks listed in this
section.
From a given set of ve traceroute trace les, all with the same destination address,
determine the number of probes per \ttl" used in each trace le,
determine whether or not the sequence of intermediate routers is the same in di erent trace
les,
if the sequence of intermediate routers is di erent in the ve trace les, list the di erence and
explain why,
if the sequence of intermediate routers is the same in the ve trace les, draw a table as shown
below (warning: the values in the table do not correspond to any trace les) to compare
the RRTs of di erent traceroute attempts. From the result, which hop is likely to incur the
maximum delay? Explain your conclusion.
TTL
Average RRT
Average RRT
Average RRT
Average RRT
Average RRT
in trace 1
in trace 2
in trace 3
in trace 4
in trace 5
1
0.5
0.7
0.8
0.7
0.9
2
0.9
1
1.2
1.2
1.3
94
3
1.5
1.5
1.5
1.5
2.5
4
2.5
2
2
2.5
3
5
3
2.5
3
3.5
3.5
6
5
4
5
4.5
4
Miscellaneous
Important! Please read!
Some intermediate router may only send back one \ICMP TTL exceeded" message for multiple
fragments of the same datagram. In this case, please use this ICMP message to calculate RTT
for all fragments. For example, Assume that the source sends Frag 1, Frag2, Frag 3 (of the
same datagram, ID: 3000). The timestamps for Frag1, Frag2, Frag3 are t1; t2; t3, respectively.
Later, the source receives one \ICMP TTL exceeded" message (ID: 3000). The timestamp is
T . Then the RRTs are calculated as: T t1, T t2, T t3.
More explanation about the output format
The number of fragments created from the original datagram is:
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The offset of the last fragment is:
If there are multiple fragmented datagrams, you need to output the above information for
each datagram. For example, assume that the source sends two datagrams: D1, D2, where
D1 and D2 are the identi cation of the two datagram. Assume that D1 has three fragments
and D2 has two fragments. Then output should be:
The number of fragments created from the original datagram D1 is: 3
112
The offset of the last fragment is: xxx.
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The number of fragments created from the original datagram D2 is: 2
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The offset of the last fragment is: yyy.
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where xxx and yyy denote the actual number calculated by your program.
If the trace le is captured in Linux, the source port number included in the original UDP
can be used to match against the ICMP error message. This is due to the special traceroute
implementation in linux, which uses UDP and ICMP. If the trace le is captured in Windows,
we should use the sequence number in the returned ICMP error message to match the sequence
number in the ICMP echo (ping) message from the source node. Note that this ICMP error
message (type 11) includes the content of the ICMP echo message (type 8) from the source.
This is due to the special traceroute implementation in Windows, which uses ICMP only
(mainly message type 8 and message type 11). It is also possible that traceroute may be
implemented in another di erent way. For instance, we have found that some traceroute
implementation allows users to select protocol among ICMP, TCP, UDP and GRE. To avoid
the unnecessary complexity of your program, you only need to handle the two scenarios
in nding a match between the original datagram and the returned ICMP error
message: either (1) use the source port number in the original UDP, or (2) use the
sequence number in the original ICMP echo message. You code should automatically
nd out the right case for matching datagrams in the trace le. We will not test your code
with a trace le not falling in the above cases.
5 Deliverables and Marking Scheme
For your nal submission of your assignment, you are required to submit your source code to connex.
You should include a readme le to tell TA how to compile and run your code. At the last lab
session that you attend, you need to demo your assignment to TAs. Nevertheless, before the nal
due date, you can still make changes on your code and submit a change.txt le to connex to describe
the changes after your demo.
The marking scheme is as follows:
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6
Components
Weight
The IP address of the source node (R1)
5
The IP address of ultimate destination node (R1)
5
The IP addresses of the intermediate destination nodes (R1)
10
The correct order of the intermediate destination nodes (R1)
5
The values in the protocol eld of IP headers (R1)
5
The number of fragments created from the original datagram (R1)
15
The o set of the last fragment (R1)
10
The avg RRTs (R1)
10
The standard deviations (R1)
5
The number of probes per ttl (R2)
10
Right answer to the second question (R2)
5
Right answer to the third/or fourth question (R2)
10
Readme.txt and change.txt(if any)
5
Total Weight
100
Plagiarism
This assignment is to be done individually. You are encouraged to discuss the design of your solution
with your classmates, but each person must implement their own assignment.
148 The End
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