simple rule help--detect unauthorized servers

["John York" <YorkJ () brcc edu>]

I need to write a rule to detect unauthorized smtp and http servers on
my network.  I have several authorized servers listed in $SMTP_SERVERS
and $HTTP_SERVERS, and a $HOME that spans 10 class C networks.  What I'd
like to do is something like this:
alert ip ($HOME AND !$SMTP_SERVERS) 25 -> any any (...

or perhaps this:
var UNAUTH_SMTP [$HOME AND !$SMTP_SERVERS]
alert ip $UNAUTH_SMTP 25 -> any any (...

Is there an easy way to do this, or do I need to create an $UNAUTH_SMTP
manually?

Thanks
John

John York
Network Engineer
Blue Ridge Community College
1 College Lane, Weyers Cave, VA 24486
540.453.2255


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