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Re: afpacket DAQ - large "Outstanding" number/percent
From: Michael Altizer <xiche () verizon net>
Date: Tue, 19 Oct 2010 01:06:44 -0400

Could you please try applying the attached patch[1] and confirming that the issue still exists? (This brings it up to the current status of the next release and fixes some rather significant issues, but does nothing to directly address the issue that you are seeing.) Also, how reproducible is the issue? What's the approximate traffic rate when this occurs? What does your BPF look like? What does your command line look like (inline mode, etc)?

In case you're wondering how the math works out, it's something like this:
1. Kernel reports 650083 packets received on the AFPacket buffer rings when queried. 2. DAQ module reports 24754 packets received in its acquire loop and passed to Snort. 3. DAQ module reports 625332 packets received in its acquire loop and fastpathed by the BPF. 4. Outstanding packets is (uint64_t) (650083 - 24754 - 625332) which is (uint64_t) (-3) which is 18446744073709551613.

So the kernel is reporting it has received three fewer packets than the DAQ has seen, which is a tad disconcerting.

-Michael

[1] patch daq-0.2/os-daq/modules/daq_afpacket.c afpacket-v3.diff

On 10/15/2010 10:49 PM, Jason Wallace wrote:
~ # snort --daq-dir /usr/lib64/daq/ --daq-list
Available DAQ modules:
pcap(v3): readback live multi unpriv
dump(v1): readback live inline multi unpriv
afpacket(v2): live inline multi unpriv


On Fri, Oct 15, 2010 at 2:07 AM, Michael Altizer<xiche () verizon net>  wrote:
  On 10/13/2010 03:11 PM, Jason Wallace wrote:
Is anyone else seeing a strange "Outstanding" number/percent after
exiting when using afpacket in passive mode? It only seems to occur in
daemon mode (-D).


Oct 13 15:05:46  snort[1331]: Can't acquire (-1) -
afpacket_daq_acquire: Poll failed: Interrupted system call!
Oct 13 15:05:47 snort[1331]:
===============================================================================
Oct 13 15:05:47 snort[1331]: Packet I/O Totals:
Oct 13 15:05:47 snort[1331]:    Received:       650083
Oct 13 15:05:47 snort[1331]:    Analyzed:        24754 (  3.808%)
Oct 13 15:05:47 snort[1331]:     Dropped:            0 (  0.000%)
Oct 13 15:05:47 snort[1331]:    Filtered:       625332 ( 96.193%)
Oct 13 15:05:47 snort[1331]: Outstanding: 18446744073709551613
(2837598287250944.000%)
Oct 13 15:05:47 snort[1331]:    Injected:            0
Oct 13 15:05:47 snort[1331]:
===============================================================================


snort # snort -V

     ,,_     -*>    Snort!<*-
    o"  )~   Version 2.9.0 (Build 68)
     ''''    By Martin Roesch&    The Snort Team:
http://www.snort.org/snort/snort-team
             Copyright (C) 1998-2010 Sourcefire, Inc., et al.
             Using libpcap version 1.0.0
             Using PCRE version: 7.9 2009-04-11
             Using ZLIB version: 1.2.3


thx,
Wally
Hi,

Please confirm that you are using the 0.2 release of LibDAQ.  There were
changes to the AFPacket code between 0.1 and 0.2 that fixed an issue
with this symptom.  You can check the version of the AFPacket DAQ module
by passing the --daq-list switch to Snort; it should be v2 if it is from
the 0.2 release.

-Michael

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Attachment: afpacket-v3.diff
Description:

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