[Snort-users] 2.1.3rc1 Performance

Darren Webb spyder007 at ...6436...
Wed May 19 22:03:02 EDT 2004

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 can
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.


-----Original Message-----
From: snort-users-admin at lists.sourceforge.net
[mailto:snort-users-admin at lists.sourceforge.net] On Behalf Of
Gary_Portnoy at ...11307...
Sent: Wednesday, May 19, 2004 2:39 PM
To: Dirk Geschke
Cc: snort-users at lists.sourceforge.net
Subject: RE: [Snort-users] 2.1.3rc1 Performance

netstat -ni reports all the packets since the last reboot, not really 
Running two instances side by side doesn't really work since i can't 
launch them both or kill them both at exactly the same time.

The only way to verify that would be to inject a known amount of packets 
on the wire and see which version reports the correct value.  Can anyon 
recommend a tool for packet generation?  I am thinking I'd like to create 
like 400,000 packets and inject them on the wire at 5mbps and see which 
version reports the truth.

Gary Portnoy

Dirk Geschke <Dirk at ...10648...>
05/19/2004 03:47 PM

        To:     Gary_Portnoy at ...11307...
        cc:     snort-users at lists.sourceforge.net
        Subject:        RE: [Snort-users] 2.1.3rc1 Performance

Hi Gary,

> The question remains however, which version is misreporting 
> statistics?
> suspect 0.8.3 since it reported 128.633% drop rate at one point.

hmm, drop/(recv+drop) shoule never exceed 100% or recv must be 

> Or is 0.8.3 just that much slower?
> Anyone care to comment?

Can you verify how many packets were really on the wire
during your snort runs?

I think 'netstat -ni' should be helpful or a parallel snoop run 
on the sniffed interface. Maybe the old libpcap returned wrong values?

Best regards


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