Yes, use the performance preprocesssor to monitor to see if you have any
dropped packets.
J
On Thu, Nov 23, 2006 at 11:12:01AM +0100, it looks like spagno_f@ifrance.com
sent me:
> Ok thank you for this hint, I will try this option.
>
> Somebody asked for a 'top' output. I will try to send this to the list, but
> as I am not onsite, it may take some time. To answer another question I had :
> no, I am not using any specific option in snort.conf. It is mainly the
> original snort.conf file. I only configured some parameters (servers...) and
> enabled/disabled some preprocessors.
>
> For Joel's question : is there any reliable way to get know much traffic is
> dropped ? Does this information appear in the output of the "performance"
> preprocessor ?
>
> Fabien
>
> Marc Norton:
> > On Snort 2.6.0, if your reassembling port 1521 traffic in stream4 you
> > might want to use the stream4 zero_flush_buffers options to wipe any
> > empty buffer space clean so you don't false positive. That often clears
> > up this symptom, its worth a shot.
> >
> > Joel Esler wrote:
> > > Are you dropping any packets? It seems that with 3 processes of Snort,
> > > on the same box, with only 2 Gigs of RAM trying to analyze that much
> > > traffic, you are probably dropping packets in addition to Snort
> > > overwriting its own memory.
> > >
> > > J
> > >
> > >
> > > On Wed, Nov 22, 2006 at 07:54:34PM +0100, it looks like
> > > spagno_f@ifrance.com sent me:
> > >
> > >> Hello,
> > >>
> > >> The machine is a dual Opteron with 2GB of RAM. It runs 3 instances of
> > >> snort. Each snort process sends logs to a specific log directory. Each
> > >> snort process has its barnyard process processing its logs/alerts to the
> > >> mysql DB. Each snort process listens on its own interface. Each
> > >> interface is attached to the SPAN port of a gigabit switch.
> > >>
> > >> Fabien
> > >>
> > >> Joel Esler:
> > >>
> > >>> How much RAM do you have in your machine?
> > >>>
> > >>> Joel
> > >>>
> > >>>
> > >>> On Tue, Nov 21, 2006 at 06:48:22PM +0100, it looks like
> > >>> spagno_f@ifrance.com sent me:
> > >>>
> > >>>> Hello,
> > >>>>
> > >>>> We encounter a strange problem with snort 2.6.0, Barnyard, BASE, all
> > >>>> compiled from source files.
> > >>>>
> > >>>> We have alerts which do not match the alert rules generating the
> > >>>> alert. Actually, by looking at the payload, we cannot find content we
> > >>>> should see. It seems several people already complained about this
> > >>>> problem before, without any real answer
> > >>>> (http://marc.theaimsgroup.com/?l=snort-users&m=112505975311791&w=2)
> > >>>>
> > >>>> Here is an example below.
> > >>>> We have this rule generating alerts we see in BASE :
> > >>>>
> > >>>> alert ip $EXTERNAL_NET any -> $HOME_NET any (msg:"SHELLCODE x86 NOOP";
> > >>>> content: "|90 90 90 90 90 90 90 90 90 90 90 90 90 90|"; depth: 128;
> > >>>> reference:arachnids,181; classtype:shellcode-detect; sid:648; rev:4;)
> > >>>>
> > >>>> Alert generated by this rule, in BASE :
> > >>>>
> > >>>> #(6 - 56146) [2006-09-29 15:27:22] [arachnids/181] [local/648]
> > >>>> [snort/:648]
> > >>>> SHELLCODE x86 NOOP
> > >>>> IPv4: 172.16.5.27 -> 172.16.5.12
> > >>>> hlen=5 TOS=0 dlen=155 ID=59197 flags=2 offset=0 TTL=128
> > >>>> chksum=45271
> > >>>> TCP: port=3563 -> dport: 1521 flags=***AP*** seq=831827579
> > >>>> ack=2816413717 off=5 res=0 win=16370 urp=0 chksum=12348
> > >>>> Payload: length = 115
> > >>>>
> > >>>> 000 : 00 73 00 00 06 00 00 00 00 00 03 5E 98 20 80 00 .s.........^.
> > >>>> ..
> > >>>> 010 : 00 06 00 00 00 00 00 00 00 00 01 0C 00 00 00 00
> > >>>> ................
> > >>>> 020 : 01 00 00 00 00 E8 03 00 00 00 00 00 00 00 00 00
> > >>>> ................
> > >>>> 030 : 00 00 00 00 00 00 01 01 00 00 00 00 00 00 00 00
> > >>>> ................
> > >>>> 040 : 01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> > >>>> ................
> > >>>> 050 : 00 00 00 00 00 00 00 00 04 00 00 00 00 00 00 00
> > >>>> ................
> > >>>> 060 : 00 00 00 00 00 00 00 00 00 00 00 00 07 05 C4 05
> > >>>> ................
> > >>>> 070 : 31 0B 07 1..
> > >>>>
> > >>>> As you can see there is no '90' bytes, as we should see in the
> > >>>> payload.
> > >>>>
> > >>>> This not the only rule with this problem. Others have the same problem
> > >>>> too (sometimes eevn preprocessors like http_inspect too).
> > >>>>
> > >>>> While looking at the ASCII dump.log file generated by barnyard I have
> > >>>> also came accross a similar exemple (below). For this alert, we should
> > >>>> see a "user" somewhere in the payload, but we don't :
> > >>>>
> > >>>>
> > >>>> [**] [1:2650:2] ORACLE user name buffer overflow attempt [**]
> > >>>> [Classification: Attempted User Privilege Gain] [Priority: 1]
> > >>>> [Xref => http://www.appsecinc.com/Policy/PolicyCheck62.html]
> > >>>> Event ID: 62662 Event Reference: 62662
> > >>>> 11/21/06-17:16:04.892127 172.16.0.136:34833 -> 172.16.5.12:1521
> > >>>> TCP TTL:64 TOS:0x0 ID:32755 IpLen:20 DgmLen:100 DF
> > >>>> ***AP*** Seq: 0xB700F908 Ack: 0xF1594793 Win: 0x3309 TcpLen: 32
> > >>>> TCP Options (3) => NOP NOP TS: 2796076485 835448929
> > >>>> 00 30 00 00 06 00 00 00 00 00 03 68 FB 01 00 00 .0.........h....
> > >>>> 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
> > >>>> 00 00 00 00 00 00 00 00 00 00 00 04 00 00 00 01 ................
> > >>>>
> > >>>> With this problem Snort becomes almost unusable since, when we try to
> > >>>> analyse an alert to see if this is a false positive or not, we cannot
> > >>>> have the correct payload which generated the alert. We don't know if
> > >>>> this is a Snort or a Barnyard problem. Unfortunately, for now, I was
> > >>>> not able to do a tcpdump of one of these packets.
> > >>>>
> > >>>> Have you noticed the same behavior ?
> > >>>>
> > >>>> What could be the cause of the problem ? What solution to apply ?
> > >>>>
> > >>>> Thank you for your help
> > >>>>
> > >>>>
> > >>>> ________________________________________________________________________
> > >>>> iFRANCE, exprimez-vous !
> > >>>> http://web.ifrance.com
> > >>>>
> > >>>> -------------------------------------------------------------------------
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> > >>>>
> > >>>> _______________________________________________
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> > >>>> Snort-users@lists.sourceforge.net
> > >>>> Go to this URL to change user options or unsubscribe:
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> > >>>>
> > >>> +---------------------------------------------------------------------+
> > >>> joel esler senior security consultant 1-706-627-2101
> > >>> Sourcefire Security for the /Real/ World -- http://www.sourcefire.com
> > >>> Snort - Open Source Network IPS/IDS -- http://www.snort.org
> > >>> gpg key: http://demo.sourcefire.com/jesler.pgp.key
> > >>> +---------------------------------------------------------------------+
> > >>>
> > >>>
> > >> ________________________________________________________________________
> > >> iFRANCE, exprimez-vous !
> > >> http://web.ifrance.com
> > >>
> > >
> > >
> > >> -------------------------------------------------------------------------
> > >> Take Surveys. Earn Cash. Influence the Future of IT
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> > >>
> > >
> > >
> > >> _______________________________________________
> > >> Snort-users mailing list
> > >> Snort-users@lists.sourceforge.net
> > >> Go to this URL to change user options or unsubscribe:
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> > >> http://www.geocrawler.com/redir-sf.php3?list=snort-users
> > >>
> > >
> > > +---------------------------------------------------------------------+
> > > joel esler senior security consultant 1-706-627-2101
> > > Sourcefire Security for the /Real/ World -- http://www.sourcefire.com
> > > Snort - Open Source Network IPS/IDS -- http://www.snort.org
> > > gpg key: http://demo.sourcefire.com/jesler.pgp.key
> > > +---------------------------------------------------------------------+
> > >
> > > -------------------------------------------------------------------------
> > > Take Surveys. Earn Cash. Influence the Future of IT
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> > > _______________________________________________
> > > Snort-users mailing list
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> > >
> > >
> >
> >
> > --
> > Marc Norton Snort Team Lead
> > Sourcefire,Inc 410-423-1924
> > www.snort.org www.sourcefire.com
> >
> >
>
>
> ________________________________________________________________________
> iFRANCE, exprimez-vous !
> http://web.ifrance.com
> -------------------------------------------------------------------------
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+---------------------------------------------------------------------+
joel esler senior security consultant 1-706-627-2101
Sourcefire Security for the /Real/ World -- http://www.sourcefire.com
Snort - Open Source Network IPS/IDS -- http://www.snort.org
gpg key: http://demo.sourcefire.com/jesler.pgp.key
+---------------------------------------------------------------------+
-------------------------------------------------------------------------
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