[Bro] Issue with Bro reporting dropped packets

Drew Dixon dwdixon at umich.edu
Thu Mar 2 14:20:37 PST 2017

First I think the recommended number of workings 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, Feb 28, 2017 at 3:20 PM, Espresso Beanies <espressobeanies at gmail.com
> wrote:

> Hi,
> I'm trying to troubleshoot a Bro IDS that is experiencing capture loss
> with dropped packets. The machine I'm using has a 16-core Intel Xeon
> processor, 96Gb RAM, and an Intel NIC. I have 3 Bro workers with CPU
> affinity enabled and I'm using the pf_ring module on CentOS with no custom
> Bro scripts running. All of my processors are running at 99% utilization.
> According to my operating system, I'm dropping about 8000 packets over the
> course of a day on a 300-400Mbps network. According to Bro capstats, I am
> dropping about the same number of packets I'm receiving, sometimes more
> than I receive. My capture_loss.log shows my workers lose about 30-50%
> packets and my manager and proxy, 70-90%. I can provide any configurations
> or screenshots if necessary.
> I'm trying to troubleshoot where the issue lies. I initially installed Bro
> with all the recommended packages (tcmalloc, etc...) and the pf_ring module
> and I can see that Bro is using it. At this point, everything I see is
> pointing to an application issue and I'm running Bro version 2.5. I had the
> same issue with Bro v.2.4 as well.
> Short of tweaking OS kernel and NIC card settings, I'm not sure where else
> I could try to reduce my packet drop count in Bro. Any recommendations?
> Thanks,
> _______________________________________________
> Bro mailing list
> bro at bro-ids.org
> http://mailman.ICSI.Berkeley.EDU/mailman/listinfo/bro
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