Not-ing out ports

[John Wiltberger <johwiltb () gmail com>]

So I have a question.  When dealing with bi-directional signatures (I know,
they aren't ideal in the least, but sometimes you can't help who develops
your signatures), if you choose to not-out a port (as in !<port number>),
does snort run a boolean OR on the traffic (as in 'if source port != <port
number OR destination port != <port number>)?

Reason is, I have a signature that's header is 'alert tcp any any <> any
!25', yet it is still alerting off of traffic over port 25.  I'm sorry if
these seems confusing, I can't think of a better way of stating this.  Any
thoughts?

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