[Snort-users] Question

Gibson, Nathan J. (HSC) Nathan-Gibson at ...15095...
Mon Jul 25 10:37:27 EDT 2011

Good info. I am running in AC.  For now I am running without the buffers. I'll take the packet loss over having snort stop running. I guess I will reevaluate my rule set to get that trimmed up.....until snort can multi thread....God I can't wait until that. 

config detection: search-method ac search-optimize

preprocessor frag3_global: max_frags 75536, memcap 143654912

preprocessor stream5_global: memcap 134217728, max_tcp 1048576, track_tcp yes, track_udp yes, track_icmp no max_active_responses 2 min_response_seconds 5,

Thanks again for all your help!

-----Original Message-----
From: Martin Holste [mailto:mcholste at ...11827...] 
Sent: Saturday, July 23, 2011 12:19 AM
To: Gibson, Nathan J. (HSC)
Cc: snort-users at lists.sourceforge.net
Subject: Re: [Snort-users] Question

Ring buffer memory is only a buffer, and a buffer will eventually fail if the CPU cannot keep up the traffic.  No matter how large the buffer, eventually it will run out because it's in a losing game.  A large buffer just buys you a few seconds before the packet loss.  One thing a lot of RAM will get you is the ability to run ac for your pattern matching engine instead of ac-split.  That will increase performance and might let your CPU keep up.

> 1. When I start with the variables (which I have been using for a year with no problem) I get no packet loss.  However the snort process just "disappears/stops after 24 hours" with no logs as to why.

Sounds like a cron job is killing it.

> 2. When I start without the variables Snort is stable but I get an average of 25% packet loss.

As I understand it, PF_RING won't use those variables anyway.  To get a look, cat /proc/net/pf_ring/<file for snort pid> which should give you the best numbers.

> Again I have 12GB of memory on this R710. I can't image why its running out of memory.  And the fact that its been running fine for a year is what's killing me. It has to be a rule causing this.
> 7/18/2011 9:33 AM :   snort[7491]: FATAL ERROR: Can't start DAQ (-1) can't mmap rx ring: Cannot allocate memory!
> PCAP_MEMORY=6120 PCAP_FRAMES=65535 /usr/local/bin/snort -c 
> /etc/snort/snort.conf -i eth1 -D

I don't think it's actually running out of memory or can't allocate it, I think it's a different problem.  What are your daq config variables?

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