Re: Certin ET rulesets and 100 percent usage.

[Matt Jonkman <jonkman () jonkmans com>]

Quick question for you Marty. Eion and Joel Esler both have made the
point that if we split the IP matching rules from a single "alert ip "
into two "alert tcp" and "alert udp" we'll get a significant performance
increase. (which I'm implementing today)

I know we'll miss icmp then, but that's not a big deal. But what causes
the performance gain here? Doesn't make sense on the surface.

Thanks!

Matt

Martin Roesch wrote:
> Yeah, you're hitting the rule chains iteratively and that's just not
> going to perform.  If you want to filter large sets of IP addresses
> that would be more properly implemented as a preprocessor with
> dedicated functionality.
>
> Marty
>
> On Thu, May 7, 2009 at 12:15 PM, Matt Jonkman <jonkman () jonkmans com> wrote:
> > Straight IP matching is something Snort doesn't do well. Unfortunately.
> > So this isn't that unexpected.
> >
> > I'd only run those rulesets where you can afford the cycles. or run a
> > second snort for these alone and turn off everything in it's config to
> > streamline some.
> >
> > Matt
> >
> > jlay () slave-tothe-box net wrote:
> > > So here's something interesting.  Enabling ANY of the below rulesets
> > > results in snort using 100% CPU:
> > >
> > > emerging-botcc.rules
> > > emerging-compromised.rules
> > > emerging-drop.rules
> > > emerging-dshield.rules
> > > emerging-rbn.rules
> > > emerging-tor.rules
> > >
> > > Without snort uses around 49%.  Using 2.8.4.1 with about 700K average
> > > traffic.  Any thoughts?  Thanks.
> > >
> > > James
> > >
> > >
> > >
> > >
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> > Emerging Threats
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> > Series Scanner you'll get full speed at 300 dpi even with all image
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-- 
--------------------------------------------
Matthew Jonkman
Emerging Threats
Phone 765-429-0398
Fax 312-264-0205
http://www.emergingthreats.net
--------------------------------------------

PGP: http://www.jonkmans.com/mattjonkman.asc



------------------------------------------------------------------------------
The NEW KODAK i700 Series Scanners deliver under ANY circumstances! Your
production scanning environment may not be a perfect world - but thanks to
Kodak, there's a perfect scanner to get the job done! With the NEW KODAK i700
Series Scanner you'll get full speed at 300 dpi even with all image 
processing features enabled. http://p.sf.net/sfu/kodak-com
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