From: Dale Shaw (dale.shaw@gmail.com)
Date: Mon Feb 09 2009 - 23:51:01 ARST
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
Blogs and organic groups at http://www.ccie.net
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