[Snort-devel] Average delay per packet observation

Patrick Mullen pmullen at sourcefire.com
Fri Jul 7 07:32:34 EDT 2017


Because of the rules option tree, your "halved" theory doesn't work.  Also,
because of the fast pattern matcher, what rules are evaluated is further
complicated.

Of greater interest is (assuming I'm reading the results correctly) is how
far different your results are for 80 rules.  How are you getting your
numbers?  How much traffic are you passing? How many iterations of your
test are you running?  With small, short tests, many things can skew
results, especially on multiuser systems.


Thanks,

Patrick

On Jul 7, 2017 4:53 AM, "Navdeep Uniyal" <Navdeep.Uniyal at neclab.eu> wrote:

> Thank you for your reply.
>
>
>
> In my case I am using a set of 5 rules repeated over(with different sid).
> So approximately each set should take the same amount of time relatively.
>
> Example: 80 rules have (16*5) rules
>
>                     40 rules have (8*5) rules
>
>                     20 rules have (4*5) rules
>
>                     10 rules have (2*5) rules
>
>
>
> By this way, I assume the delay should get halved in each case from 80 to
> 40. But this is not happening as we can see from the results. Could you
> please help me in getting the explanation.
>
>
>
>
>
> Best Regards,
>
> Navdeep
>
>
>
> *From:* Steven Sturges [mailto:ststurge at cisco.com]
> *Sent:* Mittwoch, 5. Juli 2017 13:43
> *To:* Navdeep Uniyal; snort-devel at lists.snort.org
> *Subject:* Re: [Snort-devel] Average delay per packet observation
>
>
>
> Rules are not processed sequentially.  Your expectations should depend on
> the nature of the
>
> individual rules themselves.
>
> On 7/4/17 10:16 AM, Navdeep Uniyal wrote:
>
> Hello everyone,
>
>
>
> I got some interesting results running snort (inline) for experiment with
> 80, 40, 20, 10 number of rules:
>
> All rules are matching all the incoming UDP packets. Below are the average
> delay per packet I found in the 4 experiments:
>
>
>
> 80 rules:              Average delay:  0.000680666813409 seconds
>
> 40 rules:              Average delay:  2.06440535385e-08 seconds
>
> 20 rules:              Average delay:  1.6644513569e-08   seconds
>
> 10 rules:              Average delay:  1.43723338507e-08 seconds
>
>
>
> These results are quite confusing as I expect, on decreasing from 80 to 40
> rules the average delay should be approximately halved. But I can’t see
> such behavior here.
>
>
>
> What could be the possible reason, if someone could explain.
>
>
>
>
>
>
>
> Best Regards,
>
> *Navdeep*
>
>
>
>
>
>
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