[Snort-users] Tapping into the ring buffer

sekure sekure at ...11827...
Mon Aug 22 06:16:07 EDT 2005


I was thinking of that, but ideally i was looking for something
simpler.  Besides, depending on the speed of your processor vs. the
load of the network snort might quit when it finishes processing the
last packet in the file, which could happen before tcpdump captures
its 500 Megs worth and rotates the files.

I guess I was thinking that this ring buffer has to exist somewhere in
memory, It would be nice if other applications could read it too, in
realtime.

Thanks,

On 8/19/05, Harry Hoffman <hhoffman at ...10275...> wrote:
> Hi Sekure,
> 
> Will something like this work for you:
> 
> PCAP_FRAMES=32000 /usr/sbin/tcpdump -i eth0 -C 500 -w pcap.dmp
> and then
> 
> snort -r pcap.dmp -c /etc/snort/snort.conf
> you'd need a loop for the snort bit but that should be pretty
> straightforward.
> 
> I believe that the apps are independent of each other, which is why you
> can run a host based firewall and still have snort grab all of the
> packets (someone please correct me if I'm wrong).
> 
> Also, you set the interface into promisc mode. The first application
> that does so allows any other application to not need to set promisc
> (again please correct me if I'm wrong).
> 
> 
> HTH,
> Harry
> 
> sekure wrote:
> > Snorters,
> >
> > I am running snort compiled against Phil Woods modified libpcap
> > library and I was thinking if it was possible to tap into the buffer
> > that it creates with other applications without having to recapture
> > the packets off the wire if i wanted to run some additional
> > statistical or gathering tools on them.  For example, if i run snort
> > and tcpdump side by side, on the same interface, are they both
> > grabbing packets, and is this introducing any sort of latency?  Could
> > I for example run snort and ntop and PADS (passive.sourceforge.net)
> > side by side on the same interface without introducing any more
> > slowdown (other than what is caused by processing within the
> > individual application).
> >
> > Does anyone know how much impact, if any, is introduced by running
> > additional promiscious mode applications, specifically due to
> > sniffing, or if there is any interaction at all?
> >
> > I am not 100% clear about what happens deep in the guts of the OS, so
> > i need someone to set me straight.
> >
> > Thanks in advance.
> >
> >
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