----- Original Message -----
From: "William Herrin" <bill@herrin.us>
That your computer is not globally addressable ADDS one layer of security in a process you hope has enough layers to prevent an attack from penetrating.
And make no mistake: successful security is about layers, about DEPTH. You can seek layers from other sources but a shallow security process will tend to be easily breached.
This is precisely the point I've been trying to make, and it ties in to my observations in response in the SCADA thread: not only does the number of layers matter, so does their "thickness". Certainly, if you're trying to "air-gap" a SCADA network to protect it from attack, then you are admitting a certain degree of vulnerability if your circuit passes through any sort of transport multiplexer, like a DACS, as that's a place an attacker could reconfigure to take control of your traffic. But mounting *that* attack requires insider knowledge of 4 or 5 layers of extra information which will be necessary to exploit such an attack. My estimation is that that makes that layer of your defense in depth "thicker" than some other layers might be. Those who think NAT provides no security seem still to be mounting the strawman that we think it *provides* security, rather than merely contributing some bits thereto... Cheers, -- jra -- Jay R. Ashworth Baylink jra@baylink.com Designer The Things I Think RFC 2100 Ashworth & Associates http://baylink.pitas.com 2000 Land Rover DII St Petersburg FL USA http://photo.imageinc.us +1 727 647 1274