CS 39006: Computer Networks Lab – Day 1

Who’s Who Course Instructors: Teaching Assistants: Sandip Chakraborty (Office: CSE 311, CSE Main Building) – sandipc@cse.iitkgp.ernet.in K S Rao (Office: SIT Floor, Takshashila Building) – ksrao@cse.iitkgp.ernet.in Teaching Assistants: Abhijit Mondal (PhD) Barnoprio Barua (Dual Degree) Ken Kumar (Dual Degree) Pradeep R (PhD) Saikat Biswas (PhD) Soumyajit Chatterjee (PhD) Sumitro Bhaumik (PhD) Course Website: http://cse.iitkgp.ac.in/~sandipc/Courses/CS_39006_Spring_2018.html

Lab – Dos and Don’ts Form a group of two and share the group information with Soumyajit (sjituit@gmail.com) by today, latest by January 14, 2018. The assignments need to be solved in groups. You should be there in the lab within 2:10 pm. Use the Moodle submission page to submit your assignment by the deadline. One of the members from every group can submit. Student enrolment key: STU If you face any difficulty, feel free to discuss with the instructors and the TAs. You may discuss with others over Piazza as well. You may use Internet resources. Zero tolerance against plagiarism. Plagiarized submissions will not be evaluated. Be careful before sharing your codes with others !!!

Physical Data Link Network Transport Application Assignments 8. Implementation of an application layer service 1. Network Traffic Capture and analysis Physical Data Link Network Transport Application 2. Network Traffic Capture and analysis – Go deep 3. Socket Programming – Basic client server implementation 5. Implementation of a Transport protocol 4. Socket Programming – Network application parallelization 7. Implementation of Network management and Routing functionalities 6. Implementation of a simple Routing protocol Some additional assignments may be there depending on the requirements.

Lab Evaluation and Grading Lab assignments will be evaluated by the TAs. You may discussed with the assigned TA and the course instructors in case of any doubts. Marks distribution for each assignments will be shared. Grading policies: Assignments: 40% Lab test 1: 30% (Just before or after the mid-sem) Lab test 2: 30% (Just before the end-sem) All assignments do not carry equal weights. The weight distribution among the assignments will be fixed on the day of Lab test 2 based on relative complexity.

Coming to Our Context …. Network Protocol Stack Physical Data Link Network Transport Application Software, Kernel Firmware, Device Driver Hardware

How Application Data Passes Through Different Layers Physical Data Link Network Transport Application HTTP Header HTTP Data TCP Header HTTP Header HTTP Data IP Header TCP Header HTTP Header HTTP Data MAC Header IP Header TCP Header HTTP Header HTTP Data PHY Header MAC Header IP Header TCP Header HTTP Header HTTP Data PHY Trailer

How do you access a page at www.google.com? Application Layer: Use DNS to get the IP address of the Google server - DNS returns 74.125.224.72 Application Layer: Construct an HTTP GET Request – GET 74.125.224.72/index.html HTTP/1.1 Construct an HTTP packet and forward it to the transport layer

How do you access a page at www.google.com? Transport Layer: Construct the transport layer packet (TCP packet) Source port: 3324 (port address corresponding to your browser tab) Destination port: 80 (port for a HTTP server)

How do you access a page at www.google.com? Network Layer: Construct the network layer packet (IP packet) Source IP: 172.16.22.121 (IP of your machine) Destination IP: Next hop IP for 74.125.224.72 (use the routing procedure to get this IP)

How do you access a page at www.google.com? Network Layer: Use the routing procedure to find out the next hop IP to reach the Google server at 74.125.224.72. Let this IP be 172.16.28.192 172.16.22.121 172.16.28.192 74.125.224.72

How do you access a page at www.google.com? Data Link Layer: Construct the data link layer frame from the IP datagram. How do we get destination MAC address? We need the MAC address corresponding to 172.16.28.192 Gateway 172.16.22.121 172.16.28.192 Local Area Network (LAN)

How do you access a page at www.google.com? Data Link Layer: Use ARP protocol to get the MAC address corresponding to 172.16.28.192 Gateway 172.16.22.121 172.16.28.192 Local Area Network (LAN)

Assignment 1: Understand the Packet Structure Use a packet generation tool: iperf Use a packet capture and monitoring software: tcpdump and wireshark Your task would be to capture the packets at different scenarios as explained in the assignment statement and analyze various fields in the headers. wget Iperf Client HTTP Server iperf Server

Assignment 1 Submission deadline: January 18, 2018 02:00 PM Prepare a report and submit it to Moodle by the deadline. One member of each group should submit. The report should clearly indicate the name and roll numbers of the group members.