Ethereal-users: Re: [Ethereal-users] help with filter strings

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From: Guy Harris <gharris@xxxxxxxxx>
Date: Sat, 03 Dec 2005 02:42:08 -0800
Leo Jose wrote:

I want to set a Capture Filter
1) what will be the 'Filter string ' to capture data on TCP port 7878 of my machine

As per the tcpdump/WinDump man page (for the version of tcpdump or WinDump that corresponds to the version of libpcap/WinPcap Ethereal is using), its

	tcp port 7878

2) what will be the 'Filter string' to capture data between two machines only (IP1 <-> IP2)

	host ip1 and ip2

Will the filter strings be same for the Display Filter also?

No.  They'd be

	tcp.port == 7878

and

	ip.addr == ip1 and ip.addr == ip2

For various reasons, we should probably add support for display filter that have the same syntax as capture filters (reason 1 is that you can use the same filter for both, reason 2 is that we might be able to avoid building the protocol tree for many of those filters and test the information used to generate the columns, reason 3 is that it's more obvious that the negation of "host XXX" is "not host XXX" than it is that the negation of "ip.addr == XXX" is "not (ip.addr == XXX)" and *NOT* "ip.addr != XXX", ...). We haven't done that yet, however.