Snort mailing list archives
Re: Order of stream_size and dsize checks?
From: "Joel Esler (jesler)" <jesler () cisco com>
Date: Fri, 21 Mar 2014 19:51:01 +0000
Thanks Steve. What i mean by “Faster” is, because the rules are evaluated from left to right, the faster you can make that rule fail upon evaluation, the faster the engine will run. So, basically, you can have a rule that says: dsize:320; content:”blah”; pcre:”/^blah\d4/“; or something. and while the fast pattern engine will cache “blah” to evaluate and make the rule “eligible” to be evaluated, the first option it’ll run across is “dsize”. So the engine says “does the packet equal 320?, No? okay, fail.” -- Joel Esler Open Source Manager Threat Intelligence Team Lead Vulnerability Research Team On Mar 21, 2014, at 2:58 PM, Steven Sturges <steve.sturges () sourcefire com<mailto:steve.sturges () sourcefire com>> wrote: For rules that match, all of the options will be evaluated, so no savings there, but avoiding complex checks such as PCRE is always good for performance. I'd recommend placing the options that are less likely to match on all packets except the real thing, towards the front of the rule -- taking into account any relative dependencies, of course. That is why most of the Sourcefire authored rules has flow (eg, to_server,established) as the first option. Cheers -steve On 3/21/14, 2:22 PM, snort user wrote: Joel - Could you please explain how the placing of stream_size or dsize will speed up evaluation of the rule? I can see that placing it upfront will eliminate evaluation of the more expensive options such as content or pcre, but is there some other aspect that will make the rule evaluation more faster with these rule options placed upfront? Thanks On Fri, Mar 21, 2014 at 2:11 PM, Joel Esler (jesler) <jesler () cisco com<mailto:jesler () cisco com> <mailto:jesler () cisco com>> wrote: You bring up a good point though, Harley, which is basically, if you put those checks first in the rule (before the content match) it can speed up the evaluation of the traffic by that rule. -- *Joel Esler* Open Source Manager Threat Intelligence Team Lead Vulnerability Research Team On Mar 21, 2014, at 12:06 PM, Steven Sturges <steve.sturges () sourcefire com<mailto:steve.sturges () sourcefire com> <mailto:steve.sturges () sourcefire com>> wrote: Rule options are evaluated in the order specified in the rule. On 3/21/14, 11:56 AM, Harley H wrote: Hello, Are stream_size and dsize checked following any or all content matches or are they performed first? -Harley ------------------------------------------------------------------------------ Learn Graph Databases - Download FREE O'Reilly Book "Graph Databases" is the definitive new guide to graph databases and their applications. Written by three acclaimed leaders in the field, this first edition is now available. Download your free book today! http://p.sf.net/sfu/13534_NeoTech _______________________________________________ Snort-devel mailing list Snort-devel () lists sourceforge net<mailto:Snort-devel () lists sourceforge net> <mailto: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! ------------------------------------------------------------------------------ Learn Graph Databases - Download FREE O'Reilly Book "Graph Databases" is the definitive new guide to graph databases and their applications. Written by three acclaimed leaders in the field, this first edition is now available. Download your free book today! http://p.sf.net/sfu/13534_NeoTech _______________________________________________ Snort-devel mailing list Snort-devel () lists sourceforge net<mailto:Snort-devel () lists sourceforge net> <mailto: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! ------------------------------------------------------------------------------ Learn Graph Databases - Download FREE O'Reilly Book "Graph Databases" is the definitive new guide to graph databases and their applications. Written by three acclaimed leaders in the field, this first edition is now available. Download your free book today! http://p.sf.net/sfu/13534_NeoTech _______________________________________________ Snort-devel mailing list Snort-devel () lists sourceforge net<mailto:Snort-devel () lists sourceforge net> <mailto: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<http://blog.snort.org/> for the latest news about Snort!
------------------------------------------------------------------------------ Learn Graph Databases - Download FREE O'Reilly Book "Graph Databases" is the definitive new guide to graph databases and their applications. Written by three acclaimed leaders in the field, this first edition is now available. Download your free book today! http://p.sf.net/sfu/13534_NeoTech
_______________________________________________ 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:
- Order of stream_size and dsize checks? Harley H (Mar 21)
- Re: Order of stream_size and dsize checks? Steven Sturges (Mar 21)
- Re: Order of stream_size and dsize checks? Joel Esler (jesler) (Mar 21)
- Re: Order of stream_size and dsize checks? snort user (Mar 21)
- Re: Order of stream_size and dsize checks? Steven Sturges (Mar 21)
- Re: Order of stream_size and dsize checks? Joel Esler (jesler) (Mar 21)
- Re: Order of stream_size and dsize checks? Joshua Kinard (Mar 21)
- Re: Order of stream_size and dsize checks? Joel Esler (jesler) (Mar 21)
- Re: Order of stream_size and dsize checks? Steven Sturges (Mar 21)