dump traffic on a network

-i     Listen on interface.  If unspecified, tcpdump searches the system interface list  for  the  lowest
       numbered,  configured up interface (excluding loopback).  Ties are broken by choosing the earliest
       match.

       On Linux systems with 2.2 or later kernels, an interface  argument  of  ``any''  can  be  used  to
       capture packets from all interfaces.  Note that captures on the ``any'' device will not be done in
       promiscuous mode.

       If the -D flag is supported, an interface number as printed by  that  flag  can  be  used  as  the
       interface argument.

-n     Don't convert addresses (i.e., host addresses, port numbers, etc.) to names.

-l     Make stdout line buffered.  Useful if you want to see the data while capturing it.  E.g.,
       ``tcpdump  -l  |  tee dat'' or ``tcpdump  -l   > dat  &  tail  -f  dat''.