From: mahmoud genidy (ccie.mahmoud@gmail.com)
Date: Tue Feb 10 2009 - 01:49:27 ARST
You are right Dale. I agree with you that IOS doesn't care about
time-zone names. Every thing is relative to UTC.
But when you get the task saying [ Define the PACIFIC summer-time ].
Pacific time zone regardless of its name PST or any name will be
UTC-8. And based on this time the router will calculate the moment at
which it will start the summer timing. So what I'm saying is that in
this case we have to first configure the router with Pacific time-zone
(UTC -8) before defining the summer time saving
Am I correct?
M Genidy
On 2/10/09, Dale Shaw <dale.shaw@gmail.com> wrote:
> Hi,
>
> On Tue, Feb 10, 2009 at 11:06 AM, mahmoud genidy <ccie.mahmoud@gmail.com>
> wrote:
>> If you have to configure the Day light saving say PDT, does this implies
>> you
>> have first to configure the standar time zone PST. Or there is no
>> dependency?
>
> There is no dependency.
>
> R1#sh run | i ^clock
> R1#conf t
> Enter configuration commands, one per line. End with CNTL/Z.
> R1(config)#clock summer-time PDT date 10 feb 2009 02:00 11 feb 2009 03:00
> R1(config)#end
> R1#sh clock
> *01:41:47.838 UTC Tue Feb 10 2009
> R1#clock set 01:59:30 10 feb 2009
>
> ..wait 30 seconds..
>
> R1#sh clock
> 03:00:04.731 PDT Tue Feb 10 2009
> R1#clock set 02:59:30 11 feb 2009
>
> ..wait 30 seconds..
>
> R1#sh clock
> 02:00:07.623 UTC Wed Feb 11 2009
>
> Obviously, in the real world it doesn't make a whole lot of sense to
> do it this way. Typically people either use GMT/UTC and disregard
> offsets for particular time zones and daylight savings, or apply the
> appropriate time zone/summer-time settings (zone names and offsets).
>
> Remember the "clock summer-time" configuration just applies a positive
> offset, moving time forward in the range of 1 minute to 24 hours. The
> time zone names are completely arbitrary and IOS doesn't have any
> built-in understanding of what "PST" means -- i.e. IOS doesn't know
> that PST is GMT-08:00; you have to tell it. Everything is based on the
> local clock, and offsets from the local clock.
>
> Your normal time zone could be called "MONKEYS" and your summer-time
> zone could be called "BANANAS"
>
> R1(config)#clock timezone MONKEYS 10
> R1(config)#end
> R1#sh clock
> 12:07:16.047 MONKEYS Wed Feb 11 2009
>
> On a related note, NTP is blissfully unaware of time zones and
> daylight savings too (it works in UTC) -- it's up to the operating
> system to apply offsets at the appropriate time on the appropriate
> date, if at all. This is where the "clock timezone" and "clock
> summer-time" commands come in to play.
>
> cheers,
> Dale
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