Re: Snort spikes to 100% CPU followed by network latency

["Russ Combs (rucombs)" <rucombs () cisco com>]

________________________________
From: Cody Brugh [cbrugh () gmail com]
Sent: Thursday, May 22, 2014 8:13 PM
To: snort-users () lists sourceforge net
Subject: [Snort-users] Snort spikes to 100% CPU followed by network latency

Hello,

We have been running snort in-line for over a year now with no issues in terms of latency or CPU usage.  Recently (over 
the past month) snort will all of the sudden spike CPU usage up to 100% and network latency becomes real bad, 1000+ms.

I am really not sure where to start on figuring out what is causing this.  I am starting snort so it prints the 
alerts/drops on the console and don't see any specific rule that would be causing this.

Any advise on this issue?

* Did you change your Snort version or configuration around the time you started seeing the issue?  How frequently does 
this occur?  And when it happens does it resolve itself or do you restart or what?

You can turn on PPM (config ppm ...) and enable the PPM rules (gid 134).  That may catch the problem packet which you 
can log and examine for clues.

Without any clues I'd first check for SDF and PCRE.  If you have SDF (preprocessor sensitive_data) configured you can 
try commenting that out.  If you have any pcre/O rules (PCRE override) you can try commenting those out too.

Snort OS: CentOS, 64-bit

  o"  )~   Version 2.9.6.1 GRE (Build 56)
   ''''    By Martin Roesch & The Snort Team: http://www.snort.org/snort/snort-team
           Copyright (C) 2014 Cisco and/or its affiliates. All rights reserved.
           Copyright (C) 1998-2013 Sourcefire, Inc., et al.
           Using libpcap version 1.0.0
           Using PCRE version: 7.8 2008-09-05
           Using ZLIB version: 1.2.3

DAQ version: 2.0.2

Thanks!

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