Wireshark-users: Re: [Wireshark-users] file format question
From: Stephen Fisher <steve@xxxxxxxxxxxxxxxxxx>
Date: Mon, 22 Aug 2011 14:50:01 -0600
On Mon, Aug 22, 2011 at 01:28:48PM -0700, Guy Harris wrote:

> With the "-w" flag, to get it to write out the raw packet data in pcap 
> format, rather than writing out the dissected packets as text:
> 	tcpdump -c1000 -w /tmp/tcpdump.pcap net xxx.yy.zz.0/24 

... and using "-s 0" to change the snaplen in order to capture the 
entire packets is usually desirable.  Otherwise, you'll only get the 
first 68 bytes of every packet.