[Snort-users] (no subject)

Kaplan, Andrew H. AHKAPLAN at ...10063...
Wed Nov 5 10:36:57 EST 2003

Hi J.

Regarding you question about the snort sensor, currently I have only one sensor
and that
is the actual Snort server itself monitoring traffic. I approached the webmaster
possibly installing the program on the webserver, but he wanted to adopt a wait
and see
attitude before having the program installed. 

I went ahead with re-ordering the Pass and Alert Rules sections of the
policy-based file
to experiment. Snort appears to be working well with the new order. As a further
test, I
configured all internal network traffic under the Pass rules, and commented out
the Alert
rules. The only alerts I am seeing are from machines on the internal network. 

-----Original Message-----
From: J. [mailto:jeruvy at ...9344...]
Sent: Tuesday, November 04, 2003 9:34 AM
To: Kaplan, Andrew H.
Subject: RE: [Snort-users] (no subject)

Your welcome.  Responses if any inline...

> -----Original Message-----
> From: Kaplan, Andrew H. [mailto:AHKAPLAN at ...10063...]
> Sent: Wednesday, November 05, 2003 6:30 AM
> To: 'J.'
> Cc: 'snort-users at lists.sourceforge.net'
> Subject: RE: [Snort-users] (no subject)
> J.
> Thanks for your reply. As to the policy-based.rules file, mine is
> based on the
> template found in the
> Snort 2.0 Intrusion Detection book. The approach it uses has the
> alert lines at

May I recommend "Network Intrution Detection: AN Analysts Handbook" this is
a great 'why should I get snort to do this' material....where your book is a
great 'how to setup and get running'.

> the beginning part of
> the file, with the pass rules following. According to the book, it is
> appropriate to have the alerts
> first, with the pass rules second. However, I will try your
> approach, and place
> the pass rules before
> the alerts and see where that gets me.

Yes there is even a facility within snort to change the 'order' your rules
are used, so you don't have to change your rules definitions.  Again snort
doesn't like changes to the rules, so its better to use this method than the
one you suggest.  This way rule updates also don't 'change' the method of
order accidently.

> The server in question is "outside" the firewall such that
> traffic going to its
> port, 80, goes through
> a "hole" in the wall. There are switches interposed between the
> server and the
> router. I can contact our
> network security team to get more information.

Great place to watch snort, and to deal with huge amounts of traffic.  I use
3 sensors, 2 inside subnets for monitoring traffic within, and one outside
like yours watching external port allowed traffic only.

Now do I understand you have a snort sensor on your web server?  Keep in
mind your hardware is going to be needed to be monitored to ensure you don't
run out of steam on that box.  Keep in mind snort generally cannot see
across ports on a switch, so if you have two servers for instance a mail and
a web you would probably need two sensors to see both sets of traffic.

> In response to your inquiry, I am using the book that I mentioned earlier.
> However, I am also planning on
> purchasing an additional book. My experience with this one has
> been mixed. I
> have tried to use it as much
> as possible, but I have already contacted the publisher about one
> mistake that I
> discovered. If the rules
> file approach you suggested does work, I shall be contacting the publisher
> again. I am hoping to get ano-
> ther book and be able to RTFM.

Yes there are better books out there than that one, but its still good get
up and running material.
There is many suggestions, I would recommend doing a search on amazon.com
(even if you buy elsewhere) to find some books.  Also the faq/archives
suggest some great books also.

> Thanks again for you suggestions, and I will keep you up to date.

Happy snorting!


> -----Original Message-----
> From: J. [mailto:jeruvy at ...9344...]
> Sent: Tuesday, November 04, 2003 9:24 AM
> To: Kaplan, Andrew H.
> Subject: RE: [Snort-users] (no subject)
> Are you sure your rule order is the way you want it?
> Most pass rules by default are looked at last, hence you would be seeing
> this behaviour.
> As for not seeing alerts from the internet, I'd say good great, but I
> realize you may want to look at this traffic....so what hardware are you
> using for your WAN access?
> (I also hate to say this, but have you actually read the documentation?
> These issues have been discussed and hashed so many times over the years I
> am so bored with discussing them.  As well there are some great
> books on the
> subject...)
> Note hubs work, switches don't for a rule of thumb.  There are other
> solutions but RTFM.
> J.
> > -----Original Message-----
> > From: snort-users-admin at lists.sourceforge.net
> > [mailto:snort-users-admin at lists.sourceforge.net]On Behalf Of Kaplan,
> > Andrew H.
> > Sent: Tuesday, November 04, 2003 6:10 AM
> > To: 'snort-users at lists.sourceforge.net'
> > Subject: [Snort-users] (no subject)
> >
> >
> > When writing the policy-based.rules file I had as my first lines
> > several lines
> > that read as follows:
> >
> > alert ip any any -> [any,] any
> > alert tcp any any -> [any,] any
> > alert udp any any -> [any,] any
> >
> > While these lines were uncommented, I would get an enormous
> > amount of alerts
> > from the subnet even though subsequent pass rules told
> > snort to let
> > pass any and all ip, tcp, and udp traffic on any port. Once I
> > commented out the
> > lines, the alerts dropped down to 0.
> >
> > Do I need any alert rules at the beginning of the
> > policy-based.rules file to
> > specify what subnets, in this case any subnet excluding the
> > subnet,
> > snort should alert me on? If so, what is the correct syntax?
> >
> > I did include the -o option in the command syntax. FYI syntax
> as follows:
> > 	/usr/local/bin/snort -i eth0 -c /etc/snort/snort.conf -o
> >
> > The location of the policy-based.rules file is /etc/snort
> >
> > Also, I do not seem to be getting any alerts from traffic coming
> > in from the
> > Internet. Is that normal?
> >
> >
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