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COMP9121 Assignment 2 2024 S2

In this assignment, some questions are student number dependent; you will get zero in that question if you use another student’s number.

The due date is 27 Oct 2024 at 23:59 and we will open the submission site on Canvas one week before the due date.

Submission instructions. In the “main file submission”, you can only upload your answers in a single pdf file. In the “supplementary file submission”, zip all your codes in a single zip file and submit. For Q9: you must submit your code; otherwise Q9 will not be marked. Q6: you must submit your code if you did any programming; otherwise your will not get full progress mark. This is one assignment with multiple pieces to submit. Your submission time equals to the submission time of the last piece. Late penalty will be calculated based on this submission time.

1. SDN.

11.11.44.0/24, the green path should be used;

(1) Can this load balancing function be achieved by traditional non-SDN routers? Why or why not?

(2) If SDN is used in the network, please specify the SDN switch table at w. The four interfaces (ports) of the SDN switch are labelled as I1—I4 respectively.

Please write necessary entries based on the following flow table format.

(3) Suppose there is no packet loss after round 10. In the figure, what are the congestion window sizes from round 12 to round 25?

(4) In Figure below. Two TCP (Reno) sessions are sharing the same link and the link capacity is limited by 42 segments. Whenever the sum of the congestion window sizes reaches (or exceeds) 42, a packet is lost for each TCP session and the packet loss is detected by three duplicate ACKs. TCP session 2 starts later than TCP session 1. What are the congestion window sizes of the two sessions from round 15 to round 40? If the congestion window size is not an integer (in segment), you need to round it down.

Consider the TCP procedure for estimating RTT. Let EstimatedRTT0 = 100 ms be the estimated RTT when a TCP is initialised. Then, the TCP sender receives 5 ACKs and sample RTTs are measured as SampleRTT1, SampleRTT2, SampleRTT3, SampleRTT4, and SampleRTT5. All of them are 110 ms. Let EstimatedRTTi denote the estimated RTT right after the ith ACK. We assume a = 0.125 in this question.

(3) For the formula in part (2), let n approach infinity. What is EstimatedRTTn? Comment on why this averaging procedure is called an exponential moving average.

Client C starts to request for object 1 when the main page has been successfully downloaded. It starts to request for object 2 when object 1 has been successfully downloaded. The size of the main web page is small. It fits into 1 TCP segment. Each object fits into n TCP segments, where n is the last 3 digits of your student number plus 1000. For example, if you last three digits are 123, then n = 1123. We have ssthresh=64 segments at the beginning of a TCP session. Non-persistent HTTP is used. TCP termination delay is ignored. There is no packet loss.

How long in total does it take for Client C to successfully obtain the webpage (including the main page and two objects).

(1) Use the trace files and investigate them carefully. Please write down the NAT translation table entries in the NAT router for the traffic you can find in Q5_home_side and Q5_ISP_side. Find as many entries as possible. For each entry, please give screenshots to justify your answer. (If your table has more than 5 entries, just give the screenshots for the first 5 entries in your table.) Please note that some other computers are also using the local network, and their traffic may also appear in Q5_ISP_side but not in Q5_home_side. You should ignore them when you figure out the NAT translation table.

(2) What is the MAC address of the client PC? What are the MAC addresses at the two interfaces  of the NAT router? Please give you screenshots.

6. P2P. A server distributes a file with the size of 109 bytes to n hosts. The upload rate of the server is 3.5 Mbps. The i-th host (i = 1,2,…,n) has a download rate of 0.5i Mbps. For all hosts, the upload rate is 1 Mbps. Calculate the minimum distribution time as a function of n for P2P distribution and client server distribution, and plot the two curves. (n = 1,2,…,100). You should submit your code if you did any programming to complete this task.

Assume that the one-way delay through each link inside AS1, and one-way delay through each AS outside AS1 is labeled in the figure, in ms. We assume that all dashed links have zero delay. For example, the one-way delay from Router C to AA is 30 ms. The one-way delay from Router E to Root via AS4 AS5 is 45 ms. OSPF routing protocol is used within AS1 (link cost is equivalent to one-way delay inside AS1). BGP is used among the ASes.

After resolving the IP address, Client C can visit Server A. After obtaining the main page, Client C finds that there are 2 objects to be fetched. One object is stored in Server A, but the other object is stored in Server B. Unfortunately, Client C does not know the IP address of Server B, so that Client C has to resolve the IP again.

Assumption 1: All inter-AS paths are allowed, and these inter-AS paths have been known by all routers in all ASes.

Assumption 3: Client C starts to request the IP address of object 2 when object 1 has been successfully downloaded.

Question: How long in total does it take for Client C to successfully obtain the webpage (including: DNS of main paper, download of main page, download of object 1, DNS of object 2, and download of object 2).

Q9. Hash. In this question, we aim to use SHA384 hash algorithm to find the nonce of the following magic sentence so that the hash has 6 leading zeros (24-bit zeros) in the beginning. Easy Python programming (less than 15 lines) will be needed in this question.

Here ******** indicates your student number (so this should be different for everyone) and ######## is the “nonce” you need to find. ######## is a string, which can be with any length. For example, the magic sentence below is the outcome (the answer is not unique). Please note, there is no limitations on the length of the nonce.

My number is 500123456 and I love COMP9121.22076159

You can verify it at many websites, such as, https://emn178.github.io/online-tools/sha384.html, where you can see that the hash has 6 zeros in the beginning.

10. Firewall. We will develop the firewall configuration. The figure below shows the configuration we want to achieve. The home users reside in Zone 1. The external users reside in the External Internet. A Web server (111.111.11.1) and an FTP server (111.111.11.2) are located in Zone 2. The Web server supports both http and https requests.

Complete the table to define a stateless firewall configuration for the given scenario. You can refer to the IP ranges (source and destination) by their “zone name”. Use “Ext” to indicate external Internet. Use “*” to indicate “all”.