Recitation 7 (R7)

CT 320: Network and Systems Administration

Group Work

Network Protocol Lab

The purpose of this assignment is to learn about network protocols by using a “packet sniffer” to examine network traffic on the local area network in our lab.

Description

For this assignment you will turn in a document called R7.pdf with a section for each network protocol that you capture using the packet sniffer. For this recitation we are using the tcpdump packet sniffer that is bundled with Fedora.

Part 1 – Understanding Packet Sniffers

Figure out how to run the tcpdump program by looking at the manpage and experimenting with displaying network traffic one local area network in the lab. Packet sniffers capture network traffic by listening to the interface on the local system, thus all LAN traffic is detected. Make sure you know how to specify the interface and how to dump an ASCII interpretation of the packets. The filtering mechanism in tcpdump is very useful for this assignment, since it allows the user to filter out unwanted traffic.

Part 2 – HTTP Protocol

Use tcpdump to capture an HTTP request and reply from www.google.com, without initiating any particular search, i.e. just refresh the page. Answer the following questions: What is the exact syntax of the HTTP request from the web browser host? What version of HTTP protocol is being used? What is the exact syntax of the HTTP reply from the web server? How much data is returned and what is the format? Can you see elements of the web page in the payload of the reply?

Part 3 – Network protocols

For each protocol in the following list, use tcpdump to capture the associated packets, and explain the purpose, syntax, and size of each request and reply:

1. ICMP protocol (ping command)
2. ARP protocol (arp command)
3. SSH protocol (ssh remote login)
4. SCP protocol (scp file copy)
5. NFS protocol (ls /imports; cat /imports/file1.txt)
6. DHCP protocol (ongoing broadcasts)

Part 4 – Other Protocols

Use tcpdump to find at least two other protocols that are ongoing in the network lab. What is the purpose of the protocol and who is generating it? What is the reply to the protocol from the local host, and what is the purpose?

Checkin

Submit your R7.pdf file into the drop box on RamCT for Recitation 7 (R7).