Re: [fw-wiz] Acqusition of time

From: Martin Peikert (Martin.Peikert@discon.de)
Date: 01/30/03 

From: "Martin Peikert" <Martin.Peikert@discon.de>
To: firewall-wizards@honor.icsalabs.com
Date: Thu Jan 30 09:40:21 2003

Ben Nagy wrote:
> If a firewall can't reach an NTP server because of some transient network
> condition the clock doesn't automatically go haywire - it will just start
> drifting as per the normal accuracy of the hardware clock, no?

Not necessarily. You could use clockspeed, see
http://cr.yp.to/clockspeed.html
,-----------------------------------------------------------------------
| clockspeed uses a hardware tick counter to compensate for a
| persistently fast or slow system clock. Given a few time measurements
| from a reliable source, it computes and then eliminates the clock
| skew.
`-----------------------------------------------------------------------
and
,-----------------------------------------------------------------------
| Typical success story: I started clockspeed on one of my Pentium
| computers at home on 1998-05-05. I ran sntpclock (through a 28.8
| dialup line) once on 1998-05-05 and once on 1998-05-30. On 1998-08-22,
| after no network time input for nearly three months, the clock was
| just 0.21 seconds off.
`-----------------------------------------------------------------------

So, if a firewall can't reach an NTP server a longer time, I would think
that you really have a problem ;-) But for a sufficient length of time
clockspeed will do the job and keep the time from drifting too far...

GTi

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