On Sun, 31 Dec 2000, Stephen Stuart wrote:
Date: Sun, 31 Dec 2000 14:15:59 -0800 From: Stephen Stuart <stuart@mfnx.net> To: jlewis@jasonlewis.net Cc: nanog@merit.edu Subject: Re: RFC1918 addresses to permit in for VPN?
Only that private addressing helps ensure that your machines don't have access to the Internet. If you've set up a network where there is truly no packet path to the Internet such that it wouldn't matter if your back-end network was numbered in RFC1918 space or not, then it becomes unlikely that the network in question will be compromised *by an attacker arriving via the Internet*, and your security does not depend on RFC1918 addressing. You will have someone walking up to a switch and plugging in to consider (but that's more a facility security issue). RFC1918 gives you a place to number hosts without conflicting with "public" address space, that's all.
Using RFC1918 space also gets you an IP range where the outside world has no route to it -- Sorry, but no packets are not getting there, ergo no way to hack. Assuming various things that should be standard procedure -- dynamic NAT as opposed to static, blocking source routing, etc. At that point, just by use of simple routing, you've effectively eliminated 100% of attacks from the outside, and you only have to worry about inside. The front door is secure, now work on the back door.