Re: BPF filter

["Chris Reid" <Chris.Reid () CodeCraftConsultants com>]

See:  http://www.tcpdump.org/tcpdump_man.html

Pay attention to the section OPTIONS, where it explains "expression".  To
quote this man page, a BPF filter...:

    selects  which  packets  will  be  dumped.   If  no
    expression is given, all packets on the net will be
    dumped.   Otherwise, only packets for which expres-sion
    is `true' will be dumped.


----- Original Message -----
From: "Liuhy" <solar_liu () fescomail net>
To: "snort-users" <snort-users () lists sourceforge net>
Sent: Monday, April 21, 2003 1:33 AM
Subject: [Snort-users] BPF filter


> Hello everyone,
>
>     In the option of snort command line, there is a "-F", which is
followed by a BPF filter file. I have googled it, I only know that it is
the abbreviation of "Berkley Packet Filtering", these cann't give me the
answer that I want to get. My questions are:
> 1. What is BPF filter? (not introduced in "man tcpdump", "man snort", I
cann't enter "man 4 bpf in linux)
> 2. How can I write BPF filter file? what is the rules to write it?
> 3. In snort FAQ, there is an example as following: snort <options> ``not
( (icmp[0] = 8 or icmp[0] = 0) and host <foo>)''
>     It's similar to a snort command line, is it right? what is the
relation of them?
> Thanks in advance!
>
> Liuhy
> 2003/4/21



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