In message <FB17BC57-FAB3-45E1-886A-664A0FD42C9E@delong.com>, Owen DeLong write s:
On Apr 20, 2010, at 6:34 PM, Karl Auer wrote:
On Tue, 2010-04-20 at 12:59 -0700, Owen DeLong wrote:
On Apr 20, 2010, at 12:31 PM, Roger Marquis wrote:
NAT _always_ fails-closed Stateful Inspection can be implemented fail-closed.
Not to take issue with either statement in particular, but I think there needs to be some consideration of what "fail" means.
I believe we are talking about the case where some engineer fat-fingers a change and Roger's claim is that a stateful inspection without NAT box will permit unintended traffic while a NAT box will not.
My claim is that the stateful inspection box can be implemented such that it has an equally secure set of failure modes for fat-fingering to a NAT+stateful inspection device.
Especially when the NAT/Router has a enable/disable NAT checkbox.
Reading through the security alerts from any vendor is a pretty sobering process - stuff fails open more often than you might expect.
Yep.
So I think we should be very cautious about saying that things "fail open" or "fail closed".
My point is not that they do or do not fail closed, but, that a well designed SI firewall will fail with the exact same security risks as a NAT device.
We should be especially cautious about it when the functionality we are interested in is really no more than a happy side effect of some other functionality. NAT's "security", to the extent that it exists at all, is a side effect of what it is intended to do, which is translate and map addresses.
IOW, All of NAT's security comes from the fact that it requires a state table, like stateful inspection.
Owen
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