[Snort-users] Snort home net and external net question

Jefferson, Shawn Shawn.Jefferson at ...14448...
Fri Sep 3 15:16:32 EDT 2010


You can do:
 HOME_NET [10.215.0.0/16,![10.215.40.0/24]]

but you then can't do:
EXTERNAL_NET !$HOME_NET

If you set your EXTERNAL_NET to something besides !$HOME_NET it will work of course.  I never did manage to find a way around this, and like I mentioned, I had to use multiple configs to treat a range in the middle of my home_net as external (which actually worked out much better anyway, since I could have different threshold.conf, rules, etc...)

Maybe there is a way to do it effectively/easily that I wasn't told, or could figure out at the time.

________________________________
From: Andy Berryman [mailto:aberryman at ...14765...]
Sent: Friday, September 03, 2010 11:50 AM
To: Joel Esler
Cc: snort-users at lists.sourceforge.net
Subject: Re: [Snort-users] Snort home net and external net question

Now that's just a crazy idea. Why would someone RTFM? Much easier to be lazy and ask.

/sarcasm aside


So, if I'm reading it right, I need to do something like this:

HOME_NET [10.215.0.0/16,![10.215.40.0/24]]
EXTERNAL_NET !$HOME_NET


That would include all of the 10.215.x.x as the home net except 10.215.40.x would be excluded. So then the external net !$HOME_NET should work. But it doesn't.

It's too close to holiday weekend for me to be thinking like this, brain usage stopped at 5pm Thursday.


From: Joel Esler [mailto:jesler at ...1935...]
Sent: Friday, September 03, 2010 12:42 PM
To: Andy Berryman
Cc: snort-users at lists.sourceforge.net
Subject: Re: [Snort-users] Snort home net and external net question

Check out README.variables in the doc/ directory of the tarball.


On Sep 3, 2010, at 1:01 PM, Andy Berryman wrote:

I tried that, but am getting an error. I'm running 2.8.6.0

Sep  3 16:51:33 (none) snort[18415]: FATAL ERROR: /snort/conf/general.rules(1) Negated IP ranges that are equal to or are more general than non-negated ranges are not allowed.  Consider inverting the logic: $EXTERNAL_NET.

var HOME_NET [10.215.0.0/16]
var EXTERNAL_NET [10.215.40.0/24,!$HOME_NET]

Is it b/c my home net is a /16 and the external net I'm trying to add is a /24?


Thanks,
Andy


From: Joel Esler [mailto:jesler at ...1935...]
Sent: Friday, September 03, 2010 11:53 AM
To: Andy Berryman
Cc: snort-users at lists.sourceforge.net<mailto:snort-users at ...3783...net>
Subject: Re: [Snort-users] Snort home net and external net question

On Sep 3, 2010, at 11:01 AM, Andy Berryman wrote:


If I have my home net of snort set to:

var HOME_NET [10.215.0.0/16]

How can I make my external net be !$HOME_NET and 10.215.40.0/24 subnet?


With recent versions of Snort, you can do positives and negatives in the same variable, but the more specific entry needs to come first.

var HOME_NET [10.215.0.0/16]
var EXTERNAL_NET [10.216.40.0/16,!$HOME_NET]

Should work.

Joel

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