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How to prevent the generation of inaccurate timestamps or system log messages caused by the new DST rules, outlined in the Energy Policy Act of 2005, in Catalyst switches that run Cisco IOS and CatOS system software

Core issue

In the 2007 calendar year, daylight saving time (DST) rules can cause Cisco IOS® and the Catalyst operating system (CatOS) to generate timestamps, such as those in system log messages, that are off by one hour.

In Cisco IOS, the clock summer-time zone recurring configuration command uses the United States standards for DST rules by default.

In CatOS, the set summertime enable zone configuration command and the set summertime recurring configuration command use the United States standards for DST rules by default.

The Energy Policy Act of 2005 (H.R.6.ENR), Section 110 changes the start date of DST from the first Sunday of April to the second Sunday of March, and it changes the end date from the last Sunday of October to the first Sunday of November.

These Cisco bug IDs document this issue:

Resolution

Workaround for Cisco IOS:

Use the clock summer-time configuration command in order to manually configure the proper start date and end date for DST.

clock summer-time PDT recurring2 Sun Mar 2:00 1 Sun Nov 2:00
!--- This example is for the US/Pacific time zone.

Workaround for CatOS:

Use the set summertime configuration command in order to manually configure the proper start date and end date for DST.

set summertime enable PDT
set summertime recurring
second Sunday March 02:00 first Sunday November 02:00 60
!--- This example is for the US/Pacific time zone.

Note: The use of Network Time Protocol (NTP) is not a workaround for this problem. NTP does not carry any information about time zones or summertime.

The fix does not work if the time in the configuration is modified to a date before November 6, 2006. The limitation is not present during an upgrade.

Refer to Field Notice: FN - 62613 - U.S. Daylight Savings Time Policy Changes Effective March 2007 - for Cisco IOS Software for more information.

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