Well we have known about this for quite awhile. I have mentioned it to clients and my internal support folks at my company. But wouldn’t you know it we are a day past the new Daylight Savings Time implementation and I’m getting calls and frantic people running back to my desk wondering if the sky is falling. It is funny I have had my home network (Cisco 1760, Cisco 3640, 2 x Cisco Cat 3500XL, PIX 501, 2 x Ubuntu Server, 3x Win XP Workstations, Asterisk Box, and about 5 other little project boxes in various states of not working) up to date and ready for the change for more than an month. I should mention that I missed my VX6700 WM5 phone thanks to Verizon just notifying me on friday that there was a problem. But anyway I’m going to post the work around commands and the link to Cisco’s DLST site for my reference for what will probably be a 6 month battle to find all the devices at clients that do not conform. Maybe some of you will get some millage out of it also. Good luck and fight the good fight :)
Network Time Protocol Implications
Although it might appear that the use of Network Time Protocol (NTP) will avert any issues related to these time changes, NTP and Daylight Saving Time are mutually exclusive and one does not help or hinder the other. The Network Time Protocol is a utility used to synchronize clocks on different devices. Typically, NTP takes a reference clock from a source that is based on the Coordinated Universal Time (UTC), which does not change regardless of DST.
For example, the Eastern Standard Time (EST) in the United States is five hours behind the UTC time when Daylight Saving Time is not active. EST is four hours behind when Daylight Saving Time is active. DST configuration is very specific to the time zone in which the device is deployed, and the NTP UTC is used as a reference when DST is calculated on each individual device.
Cisco IOS Software Platforms
You can change the DST configuration parameters for a system that runs Cisco IOS with a single configuration command. You can run this command at any time and on any device in order to change the current default settings of the given device.
clock summer-time zone recurring [{week} {day} {month} {hh:mm}
{week | day | month | hh:mm} [offset]]
In order to comply with the 2007 DST time change, use this command on any device that runs Cisco IOS:
clock summer-time EDT recurring 2 Sun Mar 2:00 1 Sun Nov 2:00
Cisco CatOS Platforms
You can change the DST configuration parameters for a system that runs Cisco CatOS release 5.4 and later with a single configuration command. You can run this command at any time and on any device in order to change the current default settings of the given device.
set summertime recurring [{week} {day} {month} {hh:mm}
{week | day | month | hh:mm} [offset]]
In order to comply with the 2007 DST time change, use this command on any device that runs Cisco CatOS release 5.4 and later:
set summertime enable EDT set summertime recurring second Sunday March 02:00 first Sunday November 02:00 60
Cisco PIX and ASA Platforms
You can change the DST configuration parameters for a system that runs the Cisco PIX or ASA OS with a single configuration command. You can run this command at any time and on any device in order to change the current default settings of the given device.
clock summer-time zone recurring [{week} {day} {month} {hh:mm}
{week | day | month | hh:mm} [offset]]
In order to comply with the 2007 DST time change, use this command on any device that runs the Cisco PIX or ASA OS:
clock summer-time EDT recurring 2 Sun Mar 2:00 1 Sun Nov 2:00
Note: If you do not use the summer-time option, you are not affected by this issue. To verify that you do not use the summer-time option, run this command:
Note: show run | include summer-time
If you do not receive output from this command, your device is not affected by this issue. If you receive output and your device is affected by this issue, contact the Cisco Technical Assistance Center (TAC) in order to obtain the 6.3(5.123) interim image.