Snort mailing list archives

RE: Snort with IPTables


From: "neal" <ntimm () austin rr com>
Date: Mon, 14 Jan 2002 14:15:29 -0600

I also have snort with Iptables and snort captures all my traffic even
with iptables dropping and resetting certain connections.

-----Original Message-----
From: snort-users-admin () lists sourceforge net
[mailto:snort-users-admin () lists sourceforge net] On Behalf Of Hasnain
Atique
Sent: Sunday, January 13, 2002 8:50 AM
To: Martijn Heemels; Erek Adams; Matt Kettler
Cc: Got Snort?
Subject: Re: [Snort-users] Snort with IPTables

I set up snort on my gateway running RH 7.2 and iptables, just to check
things out for myself. From what I can see so far, snort *is* seeing
things
even though iptables is blocking very many things. The gateway is
connected
directly to the cable modem, and the ISP only filters inbound 80/tcp to
prevent CR/Nimda. I initiated a nessus attack from another station and
snort
appeared to capture all.

Personally, I'm a little dumbfounded -- all this time I wasn't using
snort
on the gateway because my understanding, and pretty much all the threads
on
this list, told me snort wouldn't have visibility! Now that I think
about
it, it seems reasonable that libpcap should see the traffic whether or
not
iptables is blocking it.

-- Hasnain


----- Original Message -----
From: "Martijn Heemels" <martijn () heemels com>
To: "Erek Adams" <erek () theadamsfamily net>; "Matt Kettler"
<mkettler () evi-inc com>
Cc: "Got Snort?" <snort-users () lists sourceforge net>
Sent: Sunday, January 13, 2002 10:31 PM
Subject: RE: [Snort-users] Snort with IPTables



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Have a look at the email thread that John Sage
<jsage () finchhaven com> and I
had on this same subject a while back on the list.  IIRC, some of
his findings
seem to contradict some things that I had thought.  Now, I could
be smoking
crack, but I don't know who's right any more.  :)  Anyone want to
jump in and
save my sanity?  If not, I'm going out and have a rather good
single malt scotch.  Research shall have to wait 'till Monday!

Hi all,
I've also had an e-mail exchange with John Sage on this, following my
similar question to the list.
Since a lot is still unclear about snort's behaviour on(!) a firewall
box and I don't have the ability to test anything (I'm just a student
with one hobby server) I can only offer my personal experiences.

On my humble little server running linux-2.2.16-3 with
ipchains-1.3.9-5 and libpcap-0.6.2-7 Snort does NOT see all traffic
reaching the outside interface. The ipchains ruleset is as paranoid
as possible since a bunch of ports are open (the box has about a
dozen servers running), but only traffic targetted at open ports is
seen by snort. I get a lot of CodeRed/Nimda related activity and some
Squid proxy scans, but not much else.

The box is connected directly to a cable modem device, so there's no
switches involved. Neither is the ISP filtering any traffic (that I
know of).

I don't know enough about the layers of networking to know why my box
doesn't do what Matt's boxes do, so I'll leave that to the experts
(i.e. you).
Hope this helps build a general consensus. :-) (and ease Erek's
conscience)

G'nite for now...

and a good morning too, Erek!

-----
Erek Adams
Nifty-Type-Guy
TheAdamsFamily.Net




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