March 8, 2007
THIS FIELD NOTICE IS PROVIDED ON AN "AS IS" BASIS AND DOES NOT IMPLY ANY KIND OF GUARANTEE OR WARRANTY, INCLUDING THE WARRANTY OF MERCHANTABILITY. YOUR USE OF THE INFORMATION ON THE FIELD NOTICE OR MATERIALS LINKED FROM THE FIELD NOTICE IS AT YOUR OWN RISK. CISCO RESERVES THE RIGHT TO CHANGE OR UPDATE THIS FIELD NOTICE AT ANY TIME.
CWNCM-1.0-CON-LIC3 - 1.0
New U.S. Daylight Savings Times rules go into effect in March 2007. Consequently, customers whose network components rely on the default U.S. summertime clock settings within Cisco IOS will be affected by the following problem.
For operating systems that have not been updated with the new U.S. DST policy changes, timestamps will exhibit a one hour time clock offset lasting three weeks beginning at 2:00 A.M. on the second Sunday in March of 2007. They will also exhibit a one hour time clock offset lasting one week beginning at 2:00 A.M. on the first Sunday in November.
Display(s) will be off by one hour.
Detail Recording will be off by one hour.
System logs will be off by one hour.
If used, backups or scheduled tools will be off by one hour.
On August 8, 2005, the Energy Policy Act of 2005 (H.R.6.ENR), was signed into law. Section 110 of this Act modified the time change dates for Daylight Saving Time (DST) in the U.S.
Beginning in March of 2007, DST will begin on the second Sunday of March and end the first Sunday of November.
For 2007 and beyond, the daylight saving time period will be:
2:00 A.M. on the second Sunday in March
2:00 A.M. on the first Sunday in November
For more information on the Energy Policy Act of 2005, see H.R. 6. (See Section 110)
Impact to Networking Systems
Networking systems often make use of local time to mark logs, as well as to schedule certain events, such as IP SLA schedule starts, or the beginning or end of a time-based access-list.
In addition, inconsistencies between time zone definitions may impact event correlation systems as well as other management systems relating to problem escalation. Having accurately represented local time is a very big concern for most organizations. Local time may be reflected in logs and on phone displays. This is especially true of systems that require accurate time and time stamping for proper operations.
For networking systems, the clock or clock source is often derived from a trusted chronological source such as a private or public Atomic clock, often through Network Time Protocol (NTP). NTP communicates time in Coordinated Universal Time (UTC), colloquially known as GMT, and thus is not impacted, nor is a workaround for statutory time zone changes. Local time definitions, including summertime settings are part of the configuration of most Cisco products.
Network Time Protocol (NTP) Implications
Regardless of whether or not network components are configured to use differing clock sources such as UTC and NTP, networks will be affected when clock summer-time commands are enabled with incorrect parameters.
Initial Public Release
For More Information
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