On Tue, 15 Aug 2000 [EMAIL PROTECTED] wrote:
> Hey Team, Here is a piece of the show ver command:
>
> Atlanta_1 uptime is 10 minutes
> System restarted by watchdog timer expired at 05:59:11 pdt Tue Aug 15 2000
>
> Here's the deal. We manage net's for various clients where we get snmp
> tickets from our clients. We got one that said Cisco Up with reboot. We get
> these often but this one said the cause was due to a watchdog timer expiring.
> Nobody in the office can figure out for sure what this is. I went to CCO and
> got this from them on the watchdog timer: "Hardware or software mechanism
> that is used to trigger an event or an escape from a process unless the timer
> is periodically reset. See also watchdog."
Not Cisco-specific, but generically here's what this means.
CPU software normally runs in a closed loop. It processes tasks, performs
calculations, handles input, produces output, and goes around and around.
If the main proces gets confused or gets out of the loop, then the
machine is "hung", and performing abnormally. To get it back into a
sane state usually means turning its power on and off, hitting a hard
reset button, or similar external stimulus to re-initialize the process
and get it back on track.
A "watchdog timer" operates in somewhat the opposite manner as a live
canine watchdog. A real watchdog is asleep until it hears a burglar,
and then it wakes up and generates a stimulus such as barking.
Within the main software loop of a program, there can be written an
instruction to reset a timer to zero. If the program normally finishes
its loop and gets around to the same point once every second, then
the timer might be set to something like ten seconds, or far greater
than the normal time to compete the loop. Under normal circumstances,
the timer never runs out because it's being periodically reset by the
program.
If the program gets wedged, it will fail to repeatedly run the "reset
the watchdog" routine, the timer will expire, and when it does it will
reboot the system.
Think of it in the same terms as the heart rate monitors you see in
hospitals. (Or on TV shows of hospitals if you don't spend lots of
time in hospitals.) Under normal circumstances, the heartbeat keeps
the monitor silent. If the heartbeat stops, the alarm sounds, and
out come the guys with paddles and a jolt to reboot the patient.
Not necessarily limited to a particular flavor of router or switch,
common in many devices.
--
Jay Hennigan - Network Administration - [EMAIL PROTECTED]
NetLojix Communications, Inc. NASDAQ: NETX - http://www.netlojix.com/
WestNet: Connecting you to the planet. 805 884-6323
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