[Bro] Capture Loss

Drew Dixon dwdixon at umich.edu
Thu Mar 9 13:27:55 PST 2017

Did you search the email list already or did you just join the list?  Are
you capturing the traffic from a SPAN port or a Tap?  Is your network full
of asymmetrical traffic/routing?  Answers to these two questions first is
pretty important IMO.  I responded to a very similar question around 6 days
ago or so on list...here's what I said again:


First I think the recommended number of workers is something like number of
*real* cores (not counting hyperthreading)  -2 so for 8 *real* cores you
would use 6 workers, if you have 16 *real* cores you probably want closer
to 14 workers if this is a dedicated bro box.  Maybe try bumping up your
number of workers and enabling cpu pinning if you haven't done so.

Have you reviewed everything located here? :


Specifically a few things come to mind...I know you mentioned NIC settings
but are you sure you disabled all the NIC offloading features using
ethtool?, more detail on that at this link:


Also, wouldn't hurt to double check the the pf_ring kernel module is
loaded/loading staying loaded?  If you patch the server and the kernel gets
updated unless you have something automated to reload/reinstall the pf_ring
module you will probably need to reload the pf_ring module for the new

Also, did you configure the number of ring slots for PF_RING ?

Check to be sure that /etc/modprobe.d/pf_ring.conf exists for your PF_RING
installation...this is where you will configure the number of ring slots
for PF_RING, the default is 4096 I believe but on busy networks this needs
to be increased as appropriate (in increments of 4096)...the max value is
65534.  I would try that if you've tried everything else at the first link
above to no avail...

This is also a great resource re: PF_RING and number of ring slots:


Hope this helps,


On Tue, Mar 7, 2017 at 10:34 AM, Arash Fallah <af7 at umbc.edu> wrote:

> I'm running Bro in a clustered configuration using PF_RING to have 8
> separate workers on one box. Additionally, I have commented out almost
> everything in the default local.bro to run in Bro as efficiently as
> possible. Together, these 8 workers are using less than 20% of total CPU
> capacity.
> However, we are experiencing capture loss consistently in the 50% range,
> even though CPUs are idle 80% of the time on average.
> Does anyone have any experience with this? I would greatly appreciate the
> help.
> _______________________________________________
> Bro mailing list
> bro at bro-ids.org
> http://mailman.ICSI.Berkeley.EDU/mailman/listinfo/bro
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