tcpdump is a standard UNIX network monitoring tool that supports decoding 802.11 frame informations. Tcpdump prints out a description of the contents of packets on a network interface that match the boolean expression. 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. In all cases, only packets that match expression will be processed by tcpdump.

We will use tcpdump in this example by specifying the wireless interface ( -i ath0 ), getting extra 802.11 information (-e), and printing out hex and ASCII data from the packets (-X):

tcpdump -i ath0 -e -X

For more information checkout:-

Tcpdump: http://www.tcpdump.org/
Manpage: http://linux.die.net/man/8/tcpdump