Snort mailing list archives
Re: Snort dropping packets.
From: Phil Wood <cpw () lanl gov>
Date: Sun, 14 Jul 2002 16:38:59 -0600
On Mon, Jul 15, 2002 at 12:16:17AM +0200, Emilio Mira wrote:
I installed last libpcap version (0.7.1) from tcpdump.org after reading in the list that redhat libpcap was broken.
Are you sure that when snort compiles and loads it is using both: -l<path_to_libpcap-0.7.1> when compiling all the snort objects, and -L<path_to_libpcap-0.7.1> when loading the objects to create the snort executable? I've had the problem before when I thought ./configure had built a Makefile properly, it was actually getting the linux release version rather than the libpcap I had compiled from tcpdump.org.
Is this problem caused by Snort, libpcap or kernel?. Snort reads packets from libpcap, so whether Snort says that is processing all packets (0% drops), must be because libpcap or kernel is dropping packets. So, how could I know which one is dropping packets?.
Have you looked at /proc/net/dev and found any errors. In my case the device never has a problem. Lost packets are a result of the application not reading (vi libpcap) what the kernel has to offer in a timely manner. On a loaded link, you can expect packet loss because of the multitude of rules which require extensive pattern matching. On weekends, I don't have a problem. During the week there is enough traffic to around 0.5 percent packetloss (for the 24 hour period). If you see errors in /proc/net/dev, they will not be reflected in the data you get when snort calls pcap_stats. And, you should consider upgrading the hardware device to eliminate the problem.
On Sun, 14 Jul 2002, Matt Kettler wrote:Ok, I'll take a stab at a response. Don't use the libpcap that is supplied by RedHat if you want numbers you can trust. From what I've read, they decided to change the libpcap interfaces a bit and broke some things along the way in the process of creating a "turbo" mode or something of the like. I recall a lot of grumbling on the list about this, and I think snort includes fixes for the redhat changes, but I wouldn't trust them to work 100% since a large number of people have observed the same problems as you and reported them to the snort list. Try the official release of libpcap from tcpdump.org and see if you still have problems. (note that 0.6.2 is the latest versioned release) At 04:25 PM 7/14/2002 +0200, Emilio Mira wrote:I sent this mail few days ago, but I hadn't received any reply. It's about packets dropped by Snort. Anyone could give me a response?. Thank you. ---------- Forwarded message ---------- Date: Thu, 11 Jul 2002 12:10:20 +0200 (CEST) From: Emilio Mira <emial () alumni uv es> To: snort-users () lists sourceforge net Subject: Snort dropping packets. Hi all, I'm meassuring Snort dropped packets with 'kill -USR1 <pid>' and apparently Snort is working without drops. But if I get received packets by the interface from /proc/net/dev and processed packets from Snort with 'kill -USR1 <pid>', there are diferences (see JPG attached). Why doesn't USR1 shows me real dropped packets?. I'm using Snort 1.8.7 with default configuration and libpcap 0.7.1 on RH7.2. and an ATM interface. Thanks. -- Emilio Mira
-- Phil Wood, cpw () lanl gov ------------------------------------------------------- This sf.net email is sponsored by:ThinkGeek Welcome to geek heaven. http://thinkgeek.com/sf _______________________________________________ Snort-users mailing list Snort-users () lists sourceforge net Go to this URL to change user options or unsubscribe: https://lists.sourceforge.net/lists/listinfo/snort-users Snort-users list archive: http://www.geocrawler.com/redir-sf.php3?list=snort-users
Current thread:
- Snort dropping packets. (fwd) Emilio Mira (Jul 14)
- Re: Snort dropping packets. (fwd) Phil Wood (Jul 14)
- <Possible follow-ups>
- Re: Snort dropping packets. (fwd) Matt Kettler (Jul 14)
- Re: Snort dropping packets. Emilio Mira (Jul 14)
- Re: Snort dropping packets. Phil Wood (Jul 14)
- Re: Snort dropping packets. Emilio Mira (Jul 14)
- Re: Snort dropping packets. Emilio Mira (Jul 14)