Snort mailing list archives
Re: [Snort-sigs] Matching the beginning or end of a (preprocessor) content buffer
From: Joel Esler <jesler () sourcefire com>
Date: Fri, 9 Nov 2012 12:38:21 -0500
I suppose if your pcap was big enough, sure. For rule metrics. But not for engine performance. Two different things. Sent from my iPhone On Nov 9, 2012, at 12:23 PM, Mike Cox <mike.cox52 () gmail com> wrote:
On Fri, Nov 9, 2012 at 9:13 AM, Joel Esler <jesler () sourcefire com> wrote:On Nov 9, 2012, at 9:55 AM, Mike Cox <mike.cox52 () gmail com> wrote: So I can probably do some tests when I get the time (thanks for the responses BTW), but I'm somewhat concerned with the comment, "...it would be against static pcaps which doesn't test performance. (Some people think that looping a pcap through a system a bunch of times test performance..)" Can you elaborate on this? We've heard of people testing performance by taking a big pcap and looping it through their engine many times and thinking that's a "real world" performance test. (Which in reality, it's a test of how fast your hard drive can be read ;) I understand that using the '-r' option to tell Snort to read a pcap will not test performance of things like bandwidth, dropped packets, etc. However, in a case like this when you want to test *relative* performance between rules, is Performance Profiling not accurate for thing like avg_ticks, total_ticks, etc.? Does the engine not load the rules, build the matching data structures/logic, and process thing the same way when the '-r' option is used? Let me say again that I am asking about relative performance numbers between rules, not absolute numbers necessarily. Yeah…. ehh…. So.. Here's the deal. If you are testing a rule against a pcap that you know is going to fire, you are going to get a performance number. That performance number is relative to that pcap (No matter how big your pcap is). You can do some tweaking to a rule to get better performance against that pcap, but there is no accounting for how the rule will actually work in the real world. I'll give you a completely awful example, but I am hoping you will look past the example and not debate me on the merits of this example ;) (Not you Mike, but someone else on the list might feel like being pedantic or argumentative and do so) content:"User-Agent|3a 20|"; content:"badstuff"; You run this against any static pcap, and you will get "x" number. Then you can change the rule to read: content:"User-Agent|3a 20|": content:"badstuff|0d 0a|"; You'll get a better performance number and you'll get "y" number, which is better than "x" and think "well I improved the performance of the rule" And you did. Against that pcap. However, in the real world, your fast pattern match is "User-Agent|3a 20|" which will match on almost every http session there is.Performance can be measured in many ways and the Snort Performance Profiling takes in to account many of these. Sure, in these examples the fast-pattern matcher will default to the longest string which is, "User-Agent: ". So when you are looking at specific rule performance, I don't see how a rule that has to match on two additional bytes can be more efficient than one that doesn't (if all other things are equal).We test against pcaps all day. Constantly. Just about every rule we have in the VRT ruleset has a pcap and exploit associated with it. But it's no match for the real thing.Pcaps *are* the real thing. Again, I'm only talking about relative rule performance, not data speeds, etc.TL;DR -- You can test all you want against pcaps, at the end of the day, it's meaningless. Real World traffic mix is where it's at. You want big packets, small packets, complex packets, simple packets, etc.This is confusing. Network data is network data, no matter how it is generated ... it still sounds like using the '-r' option to tell Snort to read a pcap file is different from telling Snort to process data over an interface ('-i'). Is this right? Pcap files can contain, "big packets, small packets, complex packets, simple packets, etc." so I'm confused about the cognitive disparity here. To be clear, I'm not talking about relative performance metrics across multiple pcaps in Snort using the '-r' option, I'm talking about metrics generated by a single pcap (or a network feed from an interface), which contains data to be evaluated by the engine which is configured to use multiple rules, and those rules are the basis for the relative performance evaluations. Thanks. -Mike Cox
------------------------------------------------------------------------------ Everyone hates slow websites. So do we. Make your web apps faster with AppDynamics Download AppDynamics Lite for free today: http://p.sf.net/sfu/appdyn_d2d_nov _______________________________________________ Snort-devel mailing list Snort-devel () lists sourceforge net https://lists.sourceforge.net/lists/listinfo/snort-devel Archive: http://sourceforge.net/mailarchive/forum.php?forum_name=snort-devel Please visit http://blog.snort.org for the latest news about Snort!
Current thread:
- Matching the beginning or end of a (preprocessor) content buffer Mike Cox (Nov 07)
- Re: Matching the beginning or end of a (preprocessor) content buffer Joel Esler (Nov 08)
- Re: Matching the beginning or end of a (preprocessor) content buffer Russ Combs (Nov 08)
- Re: Matching the beginning or end of a (preprocessor) content buffer Joel Esler (Nov 08)
- Re: [Snort-sigs] Matching the beginning or end of a (preprocessor) content buffer Mike Cox (Nov 09)
- Re: [Snort-sigs] Matching the beginning or end of a (preprocessor) content buffer Joel Esler (Nov 09)
- Re: [Snort-sigs] Matching the beginning or end of a (preprocessor) content buffer Mike Cox (Nov 09)
- Re: [Snort-sigs] Matching the beginning or end of a (preprocessor) content buffer Joel Esler (Nov 09)
- Re: [Snort-sigs] Matching the beginning or end of a (preprocessor) content buffer Mike Cox (Nov 09)
- Re: [Snort-sigs] Matching the beginning or end of a (preprocessor) content buffer Russ Combs (Nov 09)
- Re: [Snort-sigs] Matching the beginning or end of a (preprocessor) content buffer Joshua Kinard (Nov 10)
- Re: Matching the beginning or end of a (preprocessor) content buffer Russ Combs (Nov 08)
- Re: Matching the beginning or end of a (preprocessor) content buffer Joel Esler (Nov 08)