Re: statistics, dropped packets, and counters

[Todd Wease <twease () sourcefire com>]

Snort gets received and drop stats from libpcap (pcap_stats() function)
which in most cases gets the stats from the kernel.

For Linux, the function pcap_stats_linux() is used as the callback for
pcap_stats() and the following comment is in the libpcap 0.9.8 code:

...
*  "ps_drop" counts packets dropped because we ran

*  out of buffer space.  It doesn't count packets

*  dropped by the interface driver.  It counts only

*  packets that passed the filter.
...

Snort uses the ps_drop stat.


Jorge Cuevas wrote:
> Hi all,
>
> I am trying to gather accurate information regarding packet lost when I 
> use snort.
>
> The point is when I send kill -USR1 signal to snort, trying to gather 
> some statistics, the dropped packets shown here are related to snort 
> itself, or  to libpcap losts (called from snort)? Is this value reliable?
>
> For example, ntop shows information regarding dropped packets due to 
> ntop application itself, and dropped packets from libpcap. In some 
> scenario, I am using pf_ring socket with ntop, and from 
> /proc/net/pf_ring, I can read libpcap or pf_ring dropping statistics 
> which fit exactly with those showed by ntop web interface. Does anyone 
> know from where I can read libpcap dropped statistics in a raw matter 
> similar to /proc/net/pf_ring ones when using snort and common libpcap? 
> ie, does libpcap log down any kind of basic or raw statistics? Are they 
> reliable?
>
> And last question, what about the statistics from this commands:
>
> ip -stats link
> cat /proc/net/dev
>
> Are the dropped packets gather from here related in any matter to 
> dropped packets shown in snort statistics?
>
> Any help will be much appreciate.
>
> Thanks in advance
>
> Jorge
>
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