[Snort-users] VRT stream5 Preprocessor Config vs Default Settings

Matt Watchinski mwatchinski at ...1935...
Fri Apr 29 10:28:41 EDT 2011


Stream5's config parser is pretty loose, so commas or spaces are ok
and can be interchanged.  This is inconsistent though in my opinion,
so I'll reformat it for the ,\ per line as suggest below so its easier
to read in 2.9.0.5 conf file for the next rule package we release.

As for the max_tcp number, being set to 8192, the CVS comments for
when this was set in the 2861 conf is that it is for memory allocation
reasons in stream5, as it pre-allocates memory per stream tracked.
Since the default is higher number, i'll up date it to reflect that
default in the 2905.conf

Thanks for the feedback.

Cheers,
-matt



On Thu, Apr 28, 2011 at 5:20 PM, Eoin Miller
<eoin.miller at ...14586...> wrote:
> VRT supplied snort.conf file that comes with 2.9.0.4 as of today contains
> this line:
>
> ---snip---
> preprocessor stream5_global: max_tcp 8192, track_tcp yes, track_udp yes,
> track_icmp no max_active_responses 2 min_response_seconds 5
> ^ ^
> |---missing commas?----|
> ---snip---
>
> I guess it still loads it with these options? If not it should look like
> (separated by line to make easier to read in the email threads):
>
> preprocessor stream5_global: max_tcp 8192,\
> track_tcp yes,\
> track_udp yes,\
> track_icmp no,\
> max_active_responses 2,\
> min_response_seconds 5
>
> Some of those settings are even less than what is turned on by default
> though it would appear. max_tcp is set to 8192 in the VRT conf as shown
> above, however the 2.9.0.5 manual states:
> --snip--
> max_tcp <num sessions> || Maximum simultaneous TCP sessions tracked. The
> default is ”262144”, maximum is ”1048576”, minimum is ”1”.
> --snip--
>
> What else is weird is that max_udp is missing in the config and therefor the
> default value of 131072 would kick in, so the VRT config has you tracking a
> lot more UDP sessions that TCP sessions with stream5. From the 2.9.0.5
> manual:
> --snip--
> max_udp <num sessions> || Maximum simultaneous UDP sessions tracked. The
> default is ”131072”, maximum is ”1048576”, minimum is ”1”.
> --snip--
>
> Not sure if this is by design or just an artifact from the previous
> snort.conf's where this has been set to this value forever in recent memory.
> Value does seem pretty low however.
>
>
> I guess something more like:
>
> preprocessor stream5_global: track_tcp yes,\
> track_udp yes,\
> track_icmp no,\
> max_active_responses 2,\
> min_response_seconds 5
>
> Or:
>
> preprocessor stream5_global: track_tcp yes,\
> max_tcp 262144,\
> track_udp yes,\
> max_udp 131072,\
> track_icmp no,\
> max_active_responses 2,\
> min_response_seconds 5
>
> Thought this might be worthy of review/consideration for others.
>
> -- Eoin
>
>
>



-- 
Matthew Watchinski
Sr. Director Vulnerability Research Team (VRT)
Sourcefire, Inc.
Office: 410-423-1928
http://vrt-blog.snort.org && http://www.snort.org/vrt/




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