tcpdump

• capture/dump network traffic
• Example: save packet data to file. Rotate file every 60 seconds

  # -n - numeric. do not convert addresses, port numbers, etc. to names
  # -i - interface to listen on. e.g. 'eth0', 'wlan0', etc. Usually defaults to all traffic minus loopback and tunnel interfaces. 
  #      Wildcard 'all' can be specified to capture all including loopback and tunnel interfaces
  # -w <filename> - save packet data to specified file. 
  # -G <n seconds> - rotate file every n seconds 
  # -z <postrotate-command> -- Used with -C or -G, will execute 'postrotate-command file' -- once each file is generated
  
  tcpdump -n -i wlan0 -w '/home/pi/tcpdump/tcpudmp.w.%Y%m%d_%H%M%S' -G 60
  

• Example: convert binary packet file to ascii

  # -q - quick mode (less infomation is printed)
  # -r <file> - read packets from file 
  
  tcpdump -n -q -i wlan0 -r <filename>