Snort mailing list archives

RE: home_net and external_net: how to use ! withmultiple subnets ?


From: "John Creegan" <jcreegan () questarweb com>
Date: Wed, 20 Aug 2003 08:00:59 -0500

Very close.  It's !$HOME_NET.

Tom Van Overbeke <tvanoverbeke () ccncsi net> 08/20/03 06:46AM >>>

on the internal side, we have various lan's / dmz's etc,
the external ip
interface (public ip adress) is connected to a hub, on
which another public
ip adress (that i also want to consider as 'home_net' is
connected.

Now i'd like to consider external net as 'everything that
is not home_net',
but i can't get the syntax right. so for the moment i have
only excluded our
main lan in external net.
the problem being that alot of false alerts are logged that
come from the
other local subnets.

this is my current definition:

var HOME_NET

[172.21.0.0/16,172.16.208.0/27,172.16.208.32/27,195.xxx.xxx.xx
x/32,195.xxx.x
xx.xxx/32]
var EXTERNAL_NET !172.21.0.0/16

Two possible minor things come to my mind:

1)  Why have you repeated 195.xxx.xxx.xxx/32 twice?  Typo I take it?

No, there's actually 2 public ip adresses listed there.


2) Wouldn't it be?
   var EXTERNAL_NET !HOME_NET

I'm not too sure about that last one, but it certainly sounds
logical.

Yes, it would seem so, but when i tried it, i got this error message:

Aug 20 13:41:06 pitbull snort: FATAL ERROR: ERROR
./snort.org-rules/bad-traffic.rules(12): Couldn't resolve hostname
HOME_NET

So it will have to be a combination of ! [] and , i'm afraid, but the
things
i tried seemed to work (no error), but didn't give the desired result.
or
maybe it's not even possible ?


anyone who's in the know, please come forward.


thx,


Tom.

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