[Oisf-users] number of alerts versus performance

Tue Jul 5 20:20:48 UTC 2016

On 01/07/16 at 14:03, Yasha Zislin wrote:
> My guess would be that the packet loss is due to the traffic type and
> home_net definition. This sensor is in management zone so it has a lot
> of Active Directory, SSH, RDP, and other management traffic. I dont
> know if this can have a negative impact on performance.

Can you share your HOME_NET definition (with example IPs)?
So far we can just guess :)

> 
> For example, I have another sensor which mostly processes HTTP/S and
> SQL/Oracle traffic with 50mil packets a minute and it only has couple
> of % of packet loss. Sam physical server with the same suricata config
> with the exception of HOME_NET
> 
> 
> ________________________________ From: Peter Manev
> <petermanev at gmail.com> Sent: Thursday, June 30, 2016 9:57 PM To: Yasha
> Zislin Cc: oisf-users at lists.openinfosecfoundation.org Subject: Re:
> [Oisf-users] number of alerts versus performance
> 
> On Thu, 2016-06-30 at 17:14 +0000, Yasha Zislin wrote:
> > More info. It seems my threads process different amount of packets.
> > It is not evenly distributed. Is there a setting somewhere for that
> > in Suricata or in PFRING? It seems that thread with 100% cpu
> > utilization changes from one to another over time. At that time I
> > notice from stats.log that new busy thread is processing more
> > packets.
> >
> 
> You mentioned earlier you were messing around with a number of diff
> settings - might be related. Did you use the irq affinity script (if
> you got an Intel nic)?
> 
> >
> >
> >
> > ______________________________________________________________________
> > From: Peter Manev <petermanev at gmail.com> Sent: Thursday, June 30,
> > 2016 4:27 PM To: Yasha Zislin Cc:
> > oisf-users at lists.openinfosecfoundation.org Subject: Re: [Oisf-users]
> > number of alerts versus performance
> >
> > On Thu, 2016-06-30 at 15:54 +0000, Yasha Zislin wrote:
> > > Peter,
> > >
> > >
> > > I found one alert that was causing high alert count. After I've
> > > disabled it, count went down but packet loss is still around 20%.
> > >
> > >
> > > my stats.log does not contain anything useful such as flow
> > > emergency mode, or ssn memcap drop. The only thing that is off is
> > > kernel
> > drops,
> > > and tcp reassembly gaps.  From my understanding kernel drops have
> > > nothing to do with Suricata and point to OS problems.
> > >
> > >
> > > I do see one of the CPUs peak at 100% when packet loss increases.
> > One
> > > thing to note. Two other CPUs are working on capturing traffic
> > > with high IRQs. My guess would be flow manager or detection
> > > engine.
> > >
> >
> >
> > You can see if you get more info from: top -H -p `pidof suricata`
> > and perf top -c cpu_number_here example: perf top -c 0
> >
> > > I dunno.
> > >
> > >
> > > Thanks
> > >
> > >
> > >
> > >
> > >
> > ______________________________________________________________________
> > > From: Peter Manev <petermanev at gmail.com> Sent: Thursday, June 30,
> > > 2016 3:00 PM To: Yasha Zislin Cc:
> > > oisf-users at lists.openinfosecfoundation.org Subject: Re:
> > > [Oisf-users] number of alerts versus performance
> > >
> > > On Thu, 2016-06-30 at 14:41 +0000, Yasha Zislin wrote:
> > > > I have been trying to figure out a packet loss on one of my
> > sensors
> > > > and I am puzzled.
> > > >
> > > > It is has 16 gigs of RAM, one quad core AMD CPU, and nic sees
> > about
> > > 3
> > > > million packets per minute. Nothing special in my mind. I am
> > > > using PFRING 6.5.0 and Suricata 3.1.
> > > >
> > > > I get about 20% to 40% packet loss.  I have another identical
> > server
> > > > which sees the same amount of traffic and maybe some of the same
> > > > traffic as well.
> > > >
> > > > I've been messing around with NIC settings, IRQs, PFRING
> > > > settings, Suricata settings trying to figure out why such a high
> > > > packet
> > loss.
> > > >
> > > >
> > > > I have just realized one big difference in these two sensors.
> > > > Problematic one gets 2k to 4k of alerts per minute which sounds
> > > huge.
> > > >
> > >
> > > Any particular sig that is alerting in excess ?
> > >
> > > > Second one gets like 80 alerts per minute. Both have the same
> > > > rulesets.
> > > >
> > > >
> > > > The difference of course is the home_net variable.
> > > >
> > > >
> > > > Can the fact that Suricata processes more rules due to HOME_NET
> > > > definition cause high performance strain on the server?
> > > >
> > >
> > > Yes HOME_NET size has effect on performance as well (among other
> > > things). For example - HOME_NET: "any" EXTERNAL_NET: "any" will
> > > certainly degrade your performance.
> > >
> > > >
> > > > If the packet does not match per HOME_NET, it will be discarded
> > > before
> > > > being processed in rules. Correct?
> > > >
> > > > Versus if packet passes HOME_NET check, it would have to go
> > through
> > > > all of the rules, hence cause higher CPU utilization.
> > > >
> > > >
> > > > Thank you for the clarification.
> > > >
> > > >
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> 
> 
> >
> >
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> >
> >
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> > >
> > >
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> > >
> > >
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> 
> -- Regards, Peter Manev
> 

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-- 
Andreas Herz