Linux Command Directory  Linux in a Nutshell    Buy it now, or
read it online on Safari Bookshelf.   tcpdump [options]
[expression]  System administration command. Dump headers and
packets of network traffic that match expression. The command
continues to capture packets until it receives a SIGTERM or
SIGINT signal (usually generated by typing the interrupt
character control-C). When finished, it will generate a report
on traffic captured, received, or dropped by the kernel.
Create matching expressions using the following primitives
followed by an ID or name.   A qualifier indicating whether to
match source or destination information. Accepted values are
src, dst, src or dst, and src and dst. When not specified, the
expression will match either source or destination traffic.   A
qualifier restricting matches to a particular kind of packet.
Accepted values are: ether, fddi, tr, wlan, ip, ip6, arp, rarp,
decnet, tcp, and udp. If not specified, the match defaults to
any appropriate protocol matching type.   A