Re: Tapping into the ring buffer

[Harry Hoffman <hhoffman () ip-solutions net>]

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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SF.Net email is Sponsored by the Better Software Conference & EXPO
September 19-22, 2005 * San Francisco, CA * Development Lifecycle Practices
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Security * Process Improvement & Measurement * http://www.sqe.com/bsce5sf
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