[Snort-users] BPF Filters

Turnbough, Bradley E. bturnbough at ...15650...
Fri Nov 14 16:25:14 EST 2014

Changing -f to -F and also updating the BPF to use 'not' instead of '!' works.

Thanks Guys.

From: James Lay [jlay at ...13475...]
Sent: Friday, November 14, 2014 3:16 PM
To: snort-users at lists.sourceforge.net
Subject: Re: [Snort-users] BPF Filters

On 2014-11-14 14:06, Turnbough, Bradley E. wrote:
> Hi All,
> I've been running snort for quite a while now with no problems.  I
> would like to set up a BPF filter to ignore ESP encapsulated traffic.
> As a test, I created a file called snort-em1.bpf and placed the
> following rule in it:
> !(src net && dst port 22)
> Then I attempted to start snort:
> /usr/sbin/snort -i em1 -u snort -g snort -c /etc/snort/snort-em1.conf
> -f /etc/snort/bpfs/snort-em1.bpf -l /var/log/snort/em1
> However, snort refuses to start:
> ERROR: Can't set DAQ BPF filter to '/etc/snort/bpfs/snort-em1.bpf'
> (pcap_daq_set_filter: pcap_compile: syntax error)!
> Can someone please help me?
> Brad

Quote it:

"not (src net and dst port 22)"

Safe some hassle and lose as many special characters as you can.  You
can test with:

/usr/sbin/snort -i em1 -u snort -g snort -c /etc/snort/snort-em1.conf
/usr/sbin/snort -i em1 -u snort -g snort -c /etc/snort/snort-em1.conf
"not (src net and dst port 22)"


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