On Sun, Nov 13, 2011 at 12:13 PM, William Herrin <bill@herrin.us> wrote:
On Sun, Nov 13, 2011 at 11:38 AM, Robert Bonomi <bonomi@mail.r-bonomi.com> wrote:
On Sun, 13 Nov 2011 10:36:43 -0500, Jason Lewis <jlewis@packetnexus.com> wrote;
http://www.redtigersecurity.com/security-briefings/2011/9/16/scada-vendors-u...
Any article that claims a /12 is a 'class B', and a /16 is a 'Class C', is DEFINITELY 'flawed'.
Hi Robert,
Give the chart a second look. 192.168.0.0/16 (one of the three RFC1918 spaces) is, in fact, a /16 of IPv4 address space and it is, in fact, found in the old "class C" range. Ditto 172.16.0.0/12. If there's a nitpick, the author should have labeled the column something like "classful area" instead of "classful description."
On Sun, Nov 13, 2011 at 10:36 AM, Jason Lewis <jlewis@packetnexus.com> wrote:
I've always looked at private IP space as more of a resource and management choice and not a security feature.
Hi Jason,
If your machine is addressed with a globally routable IP, a trivial failure of your security apparatus leaves your machine addressable from any other host in the entire world which wishes to send it packets. In the parlance, it tends to "fail open." Machines using RFC1918 or RFC4193 space often have the opposite property: a failure of the security apparatus is prone to leave them unable to interact with the rest of the world at all. They tend to "fail closed."
This "fail open" vs "fail closed" is a very good characterization of the situation. While many IPv4 situations requires RFC1918 addresses due to scarcity, so it is a moot point, this fail open vs closed argument applies very well to why one should consider IPv6 ULA addresses in certain specific scenarios. If the system does not need to speak to the outside world, a ULA is frequently the right choice to leverage this "fail closed" benefits, which IMHO outstrip any advantages due to "not having to renumber when requirements change" or whatever else the religiously anti-ULA folks have to say. CB
Think of this way: Your firewall is a deadbolt and RFC1918 is the lock on the doorknob. The knob lock doesn't stop anyone from entering an unlatched window, opening the door from the inside and walking out with all your stuff. Yet when you forget to throw the deadbolt, it does stop an intruder from simply turning the knob and wandering in.
Regards, Bill Herrin
-- William D. Herrin ................ herrin@dirtside.com bill@herrin.us 3005 Crane Dr. ...................... Web: <http://bill.herrin.us/> Falls Church, VA 22042-3004