Re: home_net and external_net: how to use ! with multiple subnets ?

[cc <cc () belfordhk com>]

Tom Van Overbeke wrote:
> Hi,
>
>
> We have installed snort on our firewall, listening on the external
> interface.
>
> 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.xxx/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?

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

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




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