Re: [fw-wiz] Acqusition of time

From: Paul D. Robertson (
Date: 01/29/03

From: "Paul D. Robertson" <>
To: Brian Monkman <>
Date: Wed Jan 29 10:28:33 2003

On Wed, 29 Jan 2003, Brian Monkman wrote:

> Folks - I'm having a discussion with a few people and we have a
> question that we are interested in getting comments from the list on.
> Are there any situations where a firewall's acqusition of time
> could/should be from a network time source? Not necessarily a public
> source, it could be an "internal" time source.

Could be, sure.

> If there are situations where this makes sense, should these same
> firewalls have battery backed up clocks on board or would that be
> unnecessary?

Imagine you had some SQL servers which got hit with a worm that
propogated, and you allowed all outbound traffic. Let's say the worm
generated enough traffic to fill up the state table on the firewall, and
due to a bug it ended up rebooting. Now, the internal network flood is
still going on. An attacker decides to take advantage of the mayhem to
launch a real attack against you, and the NTP server isn't reachable
because the switch it's sitting on has 8 vulnerable neighbors plugged into

What time gets written to the logs when the attack commences?

Worse yet, let's say it's protecting a small business or a home and
doesn't have all the good constant power that we tend to see in large

While I've often said that it's a good thing to be able to take a cheap
GPS and add a stratum 1 timeserver to a network, any time you add an
external dependency, you really, really need to think through the
scenerios, especially if you're going to have to take log files to court.

ps: Posting from home doesn't improve your odds ;)
Paul D. Robertson "My statements in this message are personal opinions which may have no basis whatsoever in fact." Director of Risk Assessment TruSecure Corporation

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