CS ASSIGNMENT – 1 SOCKET PROGRAMMING Solution

Learning Objectives

This assignment/project provides you a chance to learn about popular network, transport and application layer protocols on the Internet (User data Gram Protocol-UDP, Transmission Control Protocol-TCP, Hyper-Text Transmission Protocol-HTTP, Internet Control Message Protocol-ICMP ) and to develop services using socket programming.

    A) Network Tools [20 marks]

        1. (5 marks) DNS queries

            i. (3 points) Run “dig www.anuflora.com” from any linux based system to find the IP address of the server www.anuflora.com. [Give the screen-shot showing the output]. State the IP address of the server (2 marks). Is the server hosted inside NUS? (1 mark)
            ii. (2 points) Use dig to find the IP addresses of mail servers of the domain comp.nus.edu.sg.

        2. (5 marks) Use telnet or openssl to connect to our SMTP server (smtp.gmail.com or smtp.comp.nus.edu.sg or smtp.nus.edu.sg) other SMTP servers where you have an account. Follow the SMTP commands as given in the Luminus->Multimedia->SMTP-demo to send an email to your yahoo/gmail/hotmail account. Give the screen-shot showing the list of commands (including telnet/openssl connection line) you have used to send the mail successfully.

Tip1: NUS SMTP and POP servers require TLS/SSL. Hence, instead of Telnet, you can use "openssl". Alternatively, you can connect to other SMTP and/or POP servers.

$openssl s_client -connect smtp.gmail.com:465 -crlf -ign_eof

Tip2: Command for base64 encoding:

$echo -n "your text to encode" | base64

or use online tools like: https://www.base64encode.org/

    3. (5 marks) Use telnet or openssl to connect to our POP server (pop.nus.edu.sg) or other POP servers and access your mailbox by sending raw POP commands/messages. Retrieve the latest mail from your mailbox [Give screen shot showing your communication with POP server]. --- (Refer Appendix A for raw POP commands).

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        4. (5 marks) Use telnet ftp.ietf.org 21 (or any other FTP server; you can use openssl instead of telnet for secured connection) to connect to our ftp server and retrieve the list of files and folder inside root or any other folder. How many TCP connections are required to retrieve a file (directory listing text file or any other file)? [Give screen shot showing your communication with FTP server. Include both control connection and data connection].

    B) Socket programming (TCP)– Level 1 [10 marks]

        1. (10 marks) Develop a TCP client program using the basic c/c++ socket library to construct a http request and retrieve the file “yourip.php” from the url: http://nwtools.atwebpages.com/yourip.php or https versions at http://www.varlabs.org/yourip.php [need to handle redirect/frameset/encryption] or http://varlabs.comp.nus.edu.sg/tools/yourip.php [need to handle encryption] Parse the contents and display your current public IP address from the file returned by the server “varlabs”.

The output should be in the following format:

My public IP address is a.b.c.d

[Note: You should do the assignment by creating the proper HTTP messages as per the RFCs and using basic Socket library.]

    C) Socket programming (RAW) – Level 2 [40 marks]

        1. (25 marks) Write a c/c++ program using the basic c/c++ socket library to implement traceroute tool using TCP. The program/tool should take destination URL or IP address as input. The tool should send TCP SYN segments to the destination successively by increasing IP TTL by 1 each time. Select a destination port/service that is most possibly not running in the destination host. This will result in “host unreachable” or “port unreachable” ICMP error message. Your program should have a RAW socket to retrieve this ICMP error message. Your program should output the sender’s IP address of the ICMP error message.

            i. [25 marks] Prints list set of IP addresses from successive ICMP error messages.
            ii. [5 marks] Terminates after receiving and printing the IP address from ICMP “port unreachable” or “TCP RST” messages. If there is no ICMP or TCP RST, the program should terminate after “Time Out” without printing the destination IP.

            iii. [10 marks] Checks whether the received ICMP error messages are related to the TCP SYN packets (check only whether the reply is for TCP protocol, no need to check port number).

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Note:


        ◦ Firewalls at your laptop or router may block ICMP error messages. You may need to turn-off firewall to receive ICMP error messages.
        ◦ WINDOWS users can install VM (“VMWARE workstation Player” or Virtualbox) and then install Ubuntu/Linux on top of the VM to get Linux environment for the assignment.

        ◦ If you are using a VM to run your code, you have to turn on 'bridged connection' otherwise the ICMP packets won't be passed into the VM.
        ◦ To check – You can use tools like Wireshark (www.wireshark.org) to check whether your laptop/VM can receive ICMP error message.

    D) Parallel Web Crawler – Level 3 [30 marks]

A web crawler (or web spider) is a program that retrieves and stores pages from the Web, commonly for a Web search engine (such as Google). A parallel crawler that runs multiple processes/threads in parallel. In this assignment you will implement a parallel web crawler using the language of your choice (c, c++, java, python) that browses the WWW automatically by sending HTTP requests to many web servers in parallel. The crawler should start with a few web servers/web pages and should recursively discover more links (to more pages/servers).

Requirements

    • The crawler should store the following in a database or text file and should display them.

o URL of the web pages visited. [You can start with some known URLs in the text file/ DB and accumulate more URLs in the same text file/DB]. As parallel crawlers are accessing the text file, the access should be coordinated with proper access-lock mechanisms.
o  Response time of servers [time from sending a request to receiving the reply]
    • Try to keep the request rate of your crawler low by introducing some delay between requests. Sending request to same web server several time may result in misinterpreting the crawler as a DoS attack. If needed, you may run the crawler for long time.

    • The crawler should not make more than one request to the same web page. (Only one of the threads/process should visit. This implies the use of a common/shared database of URLs.

    • You can use high-level socket libraries (such as HttpURLConnection or HttpsURLConnection classes in Java; TLS/SSL wrapper for socket objects in Python-https://docs.python.org/3/library/ssl.html#socket-creation) for HTTP and HTTPS connections and any high-level library for parsing the contents. However, you should not call/use any existing web crawler class or tool in your application.

    • Crawler should stop after some time. (You can use any reasonable strategy to stop).

    • You are allowed to use any free/open-source classes/tools/packages for conversion (such as HTML to XML) and parsing.
    • Your codes should be well written and well commented.






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Submission:

    • All submissions should be done in respective folders of LumiNUS before due date. Late submission penalty: 10% per day.

Submission Date 1: (For Section A and B) - Wednesday 18-Sep-2019

Submit one RAR/ZIP file (change filename to your Student Number) containing one word-docx (or PDF) for Part-A and one (.c or .cpp) file for Part-B to ‘LumiNUS->Assignment1->PartAB-Submission’. In addition to solutions for Part A, the word-docx may also include instructions for compiling/running your source code.

Submission Date 2: For Section C. - Monday 30-Sep-2019

Submit one RAR/ZIP file (change filename to your Student Number) containing one word-docx (or PDF) and one (.c or .cpp) file to ‘LumiNUS->Assignment1-PartC-Submission’.

Submission Date 3: For Section D. - Wednesday 09-Oct-2019 Monday 14-Oct-2019

Submit one RAR file (change filename to your Student Number) containing one (.c or .cpp) file and one word-docx (or PDF) with instructions for compiling/running your source code to ‘LumiNUS ->Assignment1-PartD-Submission’.

If you have any question/clarification, discuss through piazza.com under the folder ‘Assignment1’.




Bhojan Anand /NUS

'Students who approach education from a deep-learning perspective make significant improvements, remember what they learn, and feel empowered to make a difference. Those who take a surface approach to learning may get good grades, but they rarely benefit much in the long term’. – from several research findings.

Learning in depth is the key focus of CS3103. Try more beyond the questions above.

[We have a Zero Tolerance for Plagiarism Policy. If you are here only for marks/grades, just let me the grade/mark you prefer to have!]


More on deep learning approach …

Students Who Take a Deep Approach--

    • Attempt to understand material for themselves

    • Seek rigorous and critical interaction with knowledge content

    • Relate ideas to previous knowledge and experience

    • Discover and use organizing principles to integrate ideas

    • Relate evidence to conclusions

    • Examine the logic of arguments



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2019/20s1    Revision date: 3-Oct-19