[Snort-users] snort inline (non-drop mode) br0

Lawrence R. Hughes, Sr. lhughes at ...14822...
Wed Feb 2 15:07:34 EST 2011


Joel,

We did a tcpdump on br0 and then looked at it with wireshark and found no dupe packets.

Thanks,
Larry

  ----- Original Message ----- 
  From: Joel Esler 
  To: Lawrence R. Hughes, Sr. 
  Cc: Jason Wallace ; snort-users at lists.sourceforge.net 
  Sent: Wednesday, February 02, 2011 12:12 PM
  Subject: Re: [Snort-users] snort inline (non-drop mode) br0


  You need to check and see if you have duplicate packet issues first.


  Then recommendations can be made after that.


  Joel


  On Wed, Feb 2, 2011 at 12:10 PM, Lawrence R. Hughes, Sr. <lhughes at ...14895...2...> wrote:

    Joel,

    Thank-you for your reply, but where do we go from here, as you well know this amount of dropped packets is not acceptable?


    Thanks,
    Larry



      ----- Original Message ----- 
      From: Joel Esler 
      To: Lawrence R. Hughes, Sr. 
      Cc: Jason Wallace ; snort-users at lists.sourceforge.net 
      Sent: Wednesday, February 02, 2011 11:50 AM
      Subject: Re: [Snort-users] snort inline (non-drop mode) br0


      Lawrence, 


      Looking at your perfmon stats, I don't see anything really crazy about your traffic.  You have lots of small packets, you have a bit of fragmentation in your packets every now and again, but nothing really out of the ordinary.


      Your session count isn't anything crazy.  I mean, it's high, but nothing I haven't seen before.


      Not sure what to tell you.  I'd check for duplicate packets (two or more copies of the same packet)  which may be the case if you are getting your traffic from a span or something.


      Joel


      On Wed, Feb 2, 2011 at 9:49 AM, Lawrence R. Hughes, Sr. <lhughes at ...391...4822...> wrote:

        Jason,

        As you suggested we added IPs for the HOME_NET and we are now using eth0.
        We are still getting about 40% dropped packets.

        Please find attached our perfmonitor file and config.


        Many Thanks,

        Larry


        ----- Original Message ----- From: "Jason Wallace" <jason.r.wallace at ...11827...>

        To: "Lawrence R. Hughes, Sr." <lhughes at ...14822...>

        Cc: "Joel Esler" <jesler at ...1935...>; <snort-users at ...2652...e.net>
        Sent: Tuesday, February 01, 2011 4:48 PM 

        Subject: Re: [Snort-users] snort inline (non-drop mode) br0


        Larry,

        In your .conf you have HOME_NET and EXTERNAL_NET set to any. You need
        to define HOME_NET with the networks/IPs you are protecting. Nearly
        every rule you are running is an "any -> any" rule. That is going to
        kill your performance.

        Start with defining your HOME_NET.

        Thx,
        Wally




        On Tue, Feb 1, 2011 at 3:42 PM, Lawrence R. Hughes, Sr.
        <lhughes at ...14822...> wrote:

          Joel,

          Sorry If I did not provide the info you need…here it is: snort 2.8.6.1

          We are experiencing a large percentage of dropped packet… dropped packets
          start very low, but on the increase all the time exceeding 70%. please see
          attached startup and perf. monitor report

          2. We see a large number of open sessions without any reduction. see
          attached perf. monitor and attached config file

          3. Only 7 rule groups are applied

          4. We have disabled many preprocessors and so rules in an attempt to
          debug the dropped packet problem??

          5. We do not detect duplicate traffic, snort is running on BR0 which
          is made of eth0 and eth1.

          6. Snort is not on a network tap…running inline without blocking.

          7. We are detecting alerts which are valid alerts.

          8. Machine is duel core, 16GB memory @1333Ghz, fSB 1333Ghz, nic on PCI
          2.0 5GBs, Raid SAS 15000RPM



          The issue is the dropped packets…..i hope the attached files provide you
          with enough info to be able to help

          Thanks,

          Larry

          ----- Original Message -----
          From: Joel Esler
          To: Lawrence R. Hughes, Sr.
          Cc: snort-users at lists.sourceforge.net
          Sent: Tuesday, February 01, 2011 1:45 PM
          Subject: Re: [Snort-users] snort inline (non-drop mode) br0
          Lawrence,
          I keep seeing you post to the list asking about open sessions. But I never
          see any responses to anyone's questions that we ask.
          Are you having a problem with open sessions, or are you perceiving it to be
          a problem? What's the problem? Are you dropping packets? Are you seeing
          duplicate traffic?
          Is Snort not detecting things? What's the issue?
          Joel

          On Tue, Feb 1, 2011 at 12:59 PM, Lawrence R. Hughes, Sr.
          <lhughes at ...14822...> wrote:


            Hi,

            We use snort inline in the non-drop mode and our sensor is listens on br0.
            Could it be that we detect the 3whs (session) with stream5, but don't
            detect when the session has ended, thus giving us a high rate of open
            sessions?

            If this is the case, then what interface would be better to use eth0 or
            eth1 (currently both eth0 & eth1 are configed to give us br0) ?

            Thanks,
            Larry


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      Joel Esler | 706-231-1451 | http://blog.snort.org | http://blog.clamav.net





  -- 
  Joel Esler | 706-231-1451 | http://blog.snort.org | http://blog.clamav.net

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