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. > > 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
