Re: snort under high density traffic

[Erek Adams <erek () snort org>]

On Sun, 10 Aug 2003, Mehmet Ersan TOPALOGLU wrote:

> I sent total of 4800000 packets to the network and snort reports at the end.
> "Snort analysed 3800000 packets out of 7000000 packets dropping ...."
> I am sure LAN is isolated no other packets can come from outside and
> $cat /proc/net/dev
> says 3800000 packet received.
>
> Story is the same when i use one packet dumper via tcpreplay at 30Mbit/s.
> Dropping packets is normal but total packets exceed with a great amount
> that sent in the LAN.
>
> What can be the reason for that?
>
> I am using Snort v1.9
> and redhat 9 linux PC with kernel 2.4.20.
> and libpcap v0.7

Upgrade.

Update Snort to 2.0.1 and lipcap to Phil Wood's patched version
[0].  What you're seeing is a known issue with older Snorts + Older pcaps
+ Linux.

Make sure you've got decent NIC's and drivers for the NICs.  Make sure the
cards are at 100 FDX, and aren't set at 10 half.  If you're seeing tons of
collisions and retransmissions then you'll "see" more than are actually
there.

Cheers!

-----
Erek Adams

   "When things get weird, the weird turn pro."   H.S. Thompson


[0]     http://public.lanl.gov/cpw/


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