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Exercise 1: nslookup
Use the nslookup command from the “Tools of the Trade” and answer the following questions:
1. Which is the IP address of the website www.koala.com.au? In your opinion, what is the reason of having several IP addresses as an output?
2. Find out the name of the IP address 127.0.0.1. What is special about this IP address?
Answer:
1.
As the image, the IP address of the www.koala.com.au is 172.67.219.46, 104.18.60.21, 104,18,61,21.
2.
Localhost. This IP address is a loopback address. Everything that send to 127.0.0.1 will send the machine itself without any external network transmissions. Can access the local website host on the local machine without the physical network interface. Ping 127.0.0.1 to test the TCP/IP work.

Exercise 2: Use ping to test host reachability
Are the following hosts reachable from your machine by using ping:
• www.unsw.edu.au
• www.getfittest.com.au
• www.mit.edu
• www.intel.com.au
• www.tpg.com.au
• www.hola.hp
• www.amazon.com
• www.tsinghua.edu.cn
• www.kremlin.ru
• 8.8.8.8
If you observe that some hosts are not reachable, then can you explain why? Check if the addresses unreachable by the ping command are reachable from the Web browser.
Answer: www.unsw.edu.au Can be reachable on ping and website.

www.getfittest.com.au Not reachable on ping and website. Unknown host. Does not exist.

www.mit.edu Can be reachable on ping and website.

www.intel.com.au Can be reachable on ping and website.

www.tpg.com.au Can be reachable on ping and website.

www.hola.hp Not reachable on ping and website. Unknown host.
Does not exist.

www.amazon.com Can be reachable on ping and website.

www.tsinghua.edu.cn Can be reachable on ping and website.

www.kremlin.ru Not reachable on ping, But reachable on web browser. Some website blocks the ping for security.

8.8.8.8 Can be reachable on ping but not on browser. It is google DNS server.

Exercise 3: Use traceroute to understand network topology
Note: Include all traceroute outputs in your report.
1. Run traceroute on your machine to www.columbia.edu . How many routers are there between your workstation and www.columbia.edu ? How many routers along the path are part of the UNSW network? Between which two routers do packets cross the Pacific
Ocean? Hint: compare the round trip times from your machine to the routers using ping.
Answer:

There are 21 routers between the CSE VLAB and www.columbia.edu.
The first five routers are part of the UNSW network. We can find the net name to determine the 1,3,4,5. As for 2, I try whois command found that is part of UNSW.

And 6th is part of aarnet.

There is a big increase on ping between 7th and 11th hops. I use ping to compare the round trip times.
7th:

8th:

9th:

10th:

So, we can found that 7th- 8th and 8th – 9th is the router cross the pacific ocean. 8th is the middle route for transiting.

2. Run traceroute from your machine to the following destinations:
(i) www.ucla.edu (ii) www.u-tokyo.ac.jp and (iii) www.lancaster.ac.uk . At which router do the paths from your machine to these three destinations diverge? Find out further details about this router. (HINT: You can find out more about a router by running the Whois command: Whois router-IP-address). Is the number of hops on each path proportional the physical distance? HINT: You can find out the geographical location of a server using the following tool – http://www.yougetsignal.com/tools/network-location/ Answer:

The first 6 hops are same. The 7th becomes different. So, the 7th router start diverging.
Those three path 7th hops all belong to aarnet. (113.197.15.149,113.197.15.147, 113.197.15.12)

www.ucla.edu

www.u-tokyo.ac.jp

www.lancaster.ac.uk

From the distance, we found that Japan is closer to Sydney compare to the Los Angeles. But the path to Los Angeles takes 13 hops. To japan takes 16 hops. Thus, the number of hops on each path is not connect with the physical distance.
3. Several servers distributed around the world provide a web interface from which you can perform a traceroute to any other host in the Internet. Here are two examples:
Answer：
IP of CSE is 129.94.242.117 IP of speedtest is 202.150.221.170 From CSE to speedtest:

From speedtest to CSE:

IP of Telstra is 203.50.5.178 From CSE to Telstra:

From Telstra to CSE:

IP of speedtest is 202.150.221.170, IP of Telstra is 203.50.5.178.
From above, the direct and reverse path pass through some same router (although name is different), but not all. Like from CSE to speedtest it passes through 202.158.194.173, but from speedtest to CSE not pass through any router with 202.158.194.xxx, same as 10.11.34.146, 206.72.210.63, etc.
But in Telstra and CSE, forward and reverse path will pass through same router again with different IP. It is for load balance and avoid conflict to allocate a different interface. That’s the reason why IP address is different.

Exercise 4: Use ping to gain insights into network performance
Note: Include all graphs in your report. You need to run the scripts (runping.sh and plot.sh) when you are physically using a lab machine or connected to a CSE server/lab machine using VLAB / VNC client. You need to ensure gnuplot and ps2pdf are available on your system if you are planning to do this exercise on your own machine.
We now use the ping utility to investigate network delay and its implications on network performance. In particular, we will analyze the dependency of packet size and delay.
follows: ./runping.sh www.abc.net (or whatever other destination you want to ping). It will automatically run ping for different packet sizes and with 50 ping packets per size. Note, since a ping is sent once per second, this script will take a few minutes to finish. Basically, this script only executes the commands:
$ ping -s 22 -c 50 -i 1 www.abc.net > www.abc.net-p50
…
$ ping -s 1472 -c 50 -i 1 www.abc.net > www.abc.net-p1500
and writes the output of the pings to the corresponding files.
Use this script for the following destinations:
(i) www.uq.edu.au (ii) www.dlsu.edu.ph and (iii) www.tu-berlin.de
In other words, execute the following commands
$ ./runping.sh www.uq.edu.au
$ ./runping.sh www.dlsu.edu.ph
$ ./runping.sh www.tu-berlin.de
In case you notice one of the hosts above is not responsive, select the following alternate destinations: (i) within Australia ( www.flinders.edu.au , www.unsw.edu.au ) (ii) Asia ( www.upm.edu.my , upd.edu.ph ) (iii) Europe ( www.aau.dk , www.uio.no )
Note that all delay values reported are in milliseconds (ms) and reflect the round trip time (RTT) between your host and the destinations.
When the runping.sh script is finished for all destinations, you can plot the results using another provided script, plot.sh , as follows:
$ ./plot.sh www.uq.edu.au-p*
$ ./plot.sh www.dlsu.edu.ph-p*
$ ./plot.sh www.tu-berlin.de-p*
If you cannot execute plot.sh, then fix the permissions by executing the following command in the command line:
$ chmod u+x plot.sh
The script plot.sh will produce the following files: destination_delay.pdf, destination_scatter.pdf, and destination_avg.txt for each of the destinations (e.g., for www.uq.edu.au we have www.uq.edu.au_delay.pdf , www.uq.edu.au_scatter.pdf and www.uq.edu.au_avg.txt ).
The graph destination_delay.pdf shows how delay varies over time (different colours correspond to different packet sizes), and destination_scatter.pdf shows delay vs. packet size as a scatter plot. destination_avg.txt contains the average (2nd column) and minimum (3rd column) delay values corresponding to each packet size (1st column).

1. For each of these locations find the (approximate) physical distance from UNSW using Google Maps and compute the shortest possible time T for a packet to reach that location from UNSW. You should assume that the packet moves (i.e. propagates) at the speed of light, 3 x 10 8 m/s. Note that the shortest possible time will simply be the distance divided by the propagation speed. Plot a graph where the x-axis represents the distance to each city (i.e. Brisbane, Manila and Berlin), and the y-axis represents the ratio between the minimum delay (i.e. RTT) as measured by the ping program (select the values for 50 byte packets) and the shortest possible time T to reach that city from UNSW. (Note that the y-values are no smaller than 2 since it takes at least 2*T time for any packet to reach the destination from UNSW and get back). Can you think of at least two reasons why the y-axis values that you plot are greater than 2?
Answer:
Speed of light : 3 x 108 m/s = 3 x 105 km/s
For www.uq.edu.au IP address is 130.102.184.3. (Brisbane)
Physical distance from UNSW (Approximate):732.39 km
Shortest possible time- T: 732.39km ÷(3 x 105km/s) ≈ 2.44𝑚𝑠
The minimum RTT (for 50byte packets) from www.uq.edu.au_avg.txt:16.987ms

For www.dlsu.edu.ph IP address is 103.231.241.180. (Manila)
Physical distance from UNSW (Approximate): 6261.82 km
Shortest possible time- T: 6261.82km÷(3 x 105km/s) ≈ 20.87𝑚𝑠
The minimum RTT (for 50byte packets) from www.dlsu.edu.ph_avg.txt:298.606ms

For www.tu-berlin.de IP address is 130.149.7.201. (Berlin)
Physical distance from UNSW (Approximate):16095.32 km
Shortest possible time- T: 16095.32km÷(3 x 105km/s) ≈ 53.65𝑚𝑠
The minimum RTT (for 50byte packets) from www.tu-berlin.de_avg.txt:273.205ms

The ratios of minimum RTT to the T.
Brisbane: 6.96 Manila: 14.30 Berlin: 5.09

The reason that ratio is always > 2.
The transmission speed does not actually reach the speed of light.
There going have delay of transmission, propagation, queuing and processing during transmission.
The RRT is the time from source to destination and back so at least at 2 * T.

2. Is the delay to the destinations constant or does it vary over time? Explain why.
Answer: www.uq.edu.au

www.dlsu.edu.ph

www.tu-berlin.de

3. Explore where the website for www.epfl.ch is hosted. Is it in Switzerland?
Answer:

For www.epfl.ch is not in Switzerland.
For www.eth.ch instead is in Switzerland.

4. The measured delay (i.e., the delay you can see in the graphs) is composed of propagation delay, transmission delay, processing delay and queuing delay. Which of these delays depend on the packet size and which do not?
Answer:
Transmission delay and Processing delay.
Transmission delay depends on packet size.
Processing delay can depend on packet size but less than transmission delay. It will check bit error.
Propagation delay depend on the physical transmission mode.
Queuing delay depend on how many packets in the queue.