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Internet Infrastructure Technologies

Assignment 1

1. [10 Marks] If a website supports HTTPS but you attempt to access it via HTTP, what will happen? Please use the Chrome/Edge browser’s built-in Developer tools (as demonstrated in the class) to capture the initial pair of HTTP request and response messages between your browser and the website of your choice. Based on it, explain what happens. (You may find more information on the Developer tools here: https://developer.chrome.com/docs/devtools/network)

2. [10 Marks] HTTP Strict Transport Security (HSTS) is a web security policy that forces browsers to connect to a website exclusively via HTTPS. What problem HSTS tries to address? Provide a screen capture of the related HTTP request and response messages (using the browser’s built-in Developer tools) that configure the browser to use HTTPS only.

3. [10 Marks] Can you find out which protocol, HTTP/1.1, HTTP/2 or HTTP/3, is (mainly) used in accessing the following websites? Please briefly describe the methodology you used to find them.

a) www.hket.com

b) www.apple.com

c) www.hku.hk

d) www.cs.hku.hk

4. [15 Marks]

a) Use nslookup to find the hostnames and IP addresses of all mail exchange servers used by domain “eee.hku.hk”. If there are more than one mail exchange servers, which one should be used first and why?

b) Use nslookup to find the hostnames and IP addresses of all name servers used by domain “eee.hku.hk”. Can you find a domain with only one name server? Why or why not?

c) From the two screen captures of nslookup for www.hku.hk and www.eee.hku.hk below, why only one case is not marked as “non-authoritative answer”? 

5. [20 Marks] While using nslookup as shown in the screen capture below, the corresponding DNS message exchanges were captured by Wireshark and stored in file dns.pcapng.

a) From the file, explain that why using “hku.hk” does not return the correct name server records? In your explanation, you can cite the frame numbers of the related DNS messages.

b) What is the size of the frame (in bytes) that carries the correct DNS reply message? Run nslookup again while changing the default/local name server to 8.8.8.8. What is the size of the frame that carries the correct DNS reply message this time? Explain the size difference (if any).