Re: Portscan preprocessors dropping packets on a simple nmap-scan

[Edin Dizdarevic <edin.dizdarevic () interActive-Systems de>]

Hi and thanks for the fast answer.

->

Ashley Thomas wrote:
> Are you referring to the packet drops reported by snort ?

Yes

> IMHO, there might be a lot of logging being done, since you are using
> nmap to generate a lot of alert causing packets; and excessive logging will
> surely overload any IDS. 

:(


> (When you disable portscan preprocessor,
> those alerts are not generated, thereby not loading the IDS)

Yes, that's clear. However, I would not expect that with about 3000
packets there are 10% packets dropped.


> How are you running snort ? (what are the options used ? )

- var $HOME_NET 192.168.25.0/24
- Logging in unified format alerts and logs
- checksum_mode none
- Order pass info alert log activation dynamic
- Preprocessor portscan (!) only

I tried also the combination stream4/conversation with slightly
better results. :(

Command line:

snort -I -D -z -c snort.conf_eth0 -i eth0 -u snort -g snort


> -Ashley
>
> Edin Dizdarevic wrote:
>
> > Hello,
> >
> > I have a strange situation here: I'm making some tests on a net
> > with heavy load. I run simple nmap X/F/N-scans having always some
> > packets dropped. I've tried 3 different NICs (Intel/3Com and
> > SIS900(Realtek)) and the problem remained. No matter which
> > portscan-preprocessor I use, some packets are dropped. Is that normal?
> > After deactivating all portscan detection everything is fine. Any docs
> > covering that?
> >
> > Regards,
> >
> > Edin

Regards,

Edin_

--
Edin Dizdarevic



-------------------------------------------------------
This SF.NET email is sponsored by: FREE  SSL Guide from Thawte
are you planning your Web Server Security? Click here to get a FREE
Thawte SSL guide and find the answers to all your  SSL security issues.
http://ads.sourceforge.net/cgi-bin/redirect.pl?thaw0026en
_______________________________________________
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