Q. For my academic project I would like to monitor and analyze data transferred via HTTP. How do I monitor HTTP Packets?
A. The easiest way is to use tcpdump program/command, which dumps traffic on a network. Tcpdump prints out the headers of packets on a network interface that match the given criteria such as monitor port 80 for http.
It can also be run with the -w flag, which causes it to save the packet data to a file for later analysis, and/or with the -r flag, which causes it to read from a saved packet file rather than to read packets from a network interface.
Type the following command at shell prompt:
# tcpdump -n -i eth0 -s 0 -w output.txt src or dst port 80
- -n : Don’t convert addresses (i.e., host addresses, port numbers, etc.) to names.
- -i eth0 : Specify interface to capture data.
- -s 0 : Snarf snaplen bytes of data from each packet rather than the default of 68. Setting to 0 means use the required length to catch whole packets.
- -w output.txt : Save data to output.txt file
- src or dst port 80 : Capture port 80.
Now open a browser and run your site and do other stuff. When finished stop tcpdump and open output.txt file for analyze data.