Ethereal-users: Re: [Ethereal-users] Writing Capture filters

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From: Guy Harris <guy@xxxxxxxxxx>
Date: Wed, 16 Apr 2003 14:55:43 -0700
On Wed, Apr 16, 2003 at 01:52:49PM -0700, Ric Rocheleau wrote:
> 	There must be some cheat sheet ot there for wring capture filters in
> Etherreal

Well, they're libpcap capture filters, and so are tcpdump filters; the
tcpdump/WinDump man page has some examples.

> 	I want to have a simple capture filter that picks up all DHCP
> traffic on some network.

If the DHCP traffic is on the standard BOOTP ports (67 and 68), you can
do

	udp port 67 or udp port 68

or, if the services database ("/etc/services" or the equivalent NIS/etc.
database on UNIX, whatever the file is on Windows) has the right
entries:

	udp port bootpc or udp port bootps