[Snort-users] 2.1.3rc1 Performance

Gary_Portnoy at ...11307... Gary_Portnoy at ...11307...
Thu May 20 09:10:06 EDT 2004

I'll know for sure tonight.  I am capturing exactly 1 million packets with 
tcpdump.  Tonight I'll connect two systems with a cross-over cable and run 
snort on one side with a stripped conf file and tcpreplay (Thanks Chad!) 
on the other side to dump out the packets.  I'll run this with both 
versions and see what gets reported.  If libpcap 0.7.2 keeps reporting 0 
dropped, I'll try to increase the rate to see if there is a point when it 
actually reports anything....

Gary Portnoy

"Kreimendahl, Chad J" <Chad.Kreimendahl at ...4716...>
05/20/2004 11:24 AM

        To:     "Darren Webb" <spyder007 at ...6436...>, <Gary_Portnoy at ...11307...>
        cc:     <snort-users at lists.sourceforge.net>
        Subject:        RE: [Snort-users] 2.1.3rc1 Performance

The problem isn't freebsd, as far as anyone can tell.  The problem appears 
to be with libpcap 0.8.3.  Using 0.7.2 resolves this reporting of dropped 
packets problem.   At this point I'm not completely sure that 0.8.3 is 
actually dropping packets, but may just be reporting drops when there are 

-----Original Message-----
From: Darren Webb [mailto:spyder007 at ...6436...] 
Sent: Wednesday, May 19, 2004 11:55 PM
To: Gary_Portnoy at ...11307...
Cc: snort-users at lists.sourceforge.net
Subject: RE: [Snort-users] 2.1.3rc1 Performance

We recently switched from Redhat based sensors to FreeBSD and noticed an
alarming jump in dropped packets as well.

You can also try this in addition to perfmon.  (FreeBSD 5.2.1 Snort 2.1.2
Libpcap 0.8.3)

Ps aux | grep snort
Kill -USR1 <pid>
Tail -100 /var/log/messages

(Of course, your commands will vary somewhat on Solaris.)

The output will show stats from when the Snort session was started.  You 
then check the frag2 and stream4 preprocessors for possible memory faults
and discarded packets.  We were seeing 40% to 80% packet loss at times and
by giving these preprocessors extra memory and defining the TTLs better in
the snort.conf file we are now at 1% or lower.

Hope this helps some.


This message is for the named person's use only. This communication is for 
informational purposes only and has been obtained from sources believed to 
be reliable, but it is not necessarily complete and its accuracy cannot be 
guaranteed. It is not intended as an offer or solicitation for the purchase
or sale of any financial instrument or as an official confirmation of any
transaction. Moreover, this material should not be construed to contain any
recommendation regarding, or opinion concerning, any security. It may
contain confidential, proprietary or legally privileged information. No
confidentiality or privilege is waived or lost by any mistransmission. If
you receive this message in error, please immediately delete it and all
copies of it from your system, destroy any hard copies of it and notify the
sender. You must not, directly or indirectly, use, disclose, distribute, 
print, or copy any part of this message if you are not the intended 
recipient.  Any views expressed in this message are those of the individual
sender, except where the message states otherwise and the sender is 
authorized to state them to be the views of any such entity.

ITG Inc. reserves the right to monitor and archive all electronic 
communications through its network. 

ITG Inc. Member NASD, SIPC

More information about the Snort-users mailing list