Prepare Cisco devices for Daylight Saving Time changes

by David "Davis CCIE, MCSE+I, SCSA" | Feb 22, 2007 9:29:00 PM

Tags: David Davis CCIE, MCSE+I, SCSA, Daylight Saving Time, Cisco Systems Inc., Cisco-device, Cisco IOS, router, Cisco Routers and Management Newsletter

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Takeaway: Daylight Saving Time comes early this year: Are your Cisco devices ready for the change? David Davis tells you two ways to make sure your Cisco routers and switches reflect the correct time after March 11.

The word is out about Daylight Saving Time (DST). In case you've missed it, the DST schedule changes this year, thanks to the Energy Policy Act of 2005. This year, DST begins on March 11, three weeks earlier than usual. (It also ends one week later�on November 4.)

These changes have the potential to wreak havoc on systems throughout the country. However, as long as you understand the effects and your options, you should be fine.

Of course, it helps to know how to configure your router's time in the first place. For a quick review, check out "Properly set a Cisco router's clock and time zone," which also addresses DST settings.

Now, back to the DST changes: The schedule shift could significantly impact operations, including Cisco routers and switches. While an hour may not seem like a big deal, don't underestimate the power of 60 minutes. Incorrect time can affect authentication systems, logging systems, and more.

The DST changes may or may not be a problem for you depending on which Cisco features you use. Here are some of the Cisco features that use local time:

Some of the built-in VoIP Call Manager functions
System logs
Time-based routing
Cisco IOS kron jobs
Time-based access control lists

Of course, these are just some examples. There may be other functions that an incorrect time will affect.

In addition, don't think that you're in the clear because you use an NTP server for your device's time. NTP servers use Universal Time�the Cisco device adjusts this time based on the time zone you've configured.

To adequately prepare your Cisco devices for the DST changes, you have two options.

Option 1

Upgrade your Cisco IOS to a newer version that addresses these changes. Once you install the IOS and reboot, you should be good to go. The Cisco Upgrade Planner (registration required) can help you find the right IOS version.

However, if you have more than a few routers and switches, this could be a painful solution for a potentially minor issue. In other words, the cure could be worse than the ailment. Then again, you're going to need to upgrade sooner or later anyway.

Option 2

Of course, there's a much less painful option�and it's one you can complete manually with a single command:

clock summer-time CDT recurring 2 Sun Mar 2:00 1 Sun Nov 2:00

Entering this command on all routers and switches will manually tell the devices which day and which time to "spring forward" and "fall back." One caveat: This command is for the Central Time Zone, so make adjustments according.

More information

Keep in mind that Cisco devices aren't the only ones affected by the DST changes. Check out these TechRepublic resources:

Have you prepared your systems and devices for the DST changes? Share your thoughts in this article's discussion.

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David Davis has worked in the IT industry for 12 years and holds several certifications, including CCIE, MCSE+I, CISSP, CCNA, CCDA, and CCNP. He currently manages a group of systems/network administrators for a privately owned retail company and performs networking/systems consulting on a part-time basis.

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